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SPOT Satellite Personal Tracker - Full Review

Does this highly anticipated technological breakthrough live up to the hype?

Overall Rating: Unrated

Due to the complex nature of the SPOT system, which includes the actual SPOT unit, all the systems downstream of the SPOT unit that must function without error to successfully deliver a message, the broad range of conditions under which the unit may be used, and each user's expectations of reliability and risk level, we cannot rate this product. It is up to each potential user to determine how appropriate the SPOT unit will be for their communication needs in the conditions they expect to use it.

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by Alan Dixon and Roger Caffin, with assistance from the other members of the SPOT testing team: Mike Martin and Steve Nelson. |


SPOT Satellite Personal Tracker - Full Review - 1
The SPOT Satellite Messenger (SPOT unit).

The SPOT unit has the potential to be a breakthrough in backcountry safety. It's lighter, more compact, and less expensive than Personal Locator Beacons (PLBs), which can only transmit a distress signal to emergency services. It's lighter and less expensive than a satellite phone and has more coverage than a cell phone. The SPOT also has a Tracking (breadcrumb) mode, which automatically sends your location every ten minutes. Unlike PLBs (or even most cell or satellite phones), the SPOT unit can transmit your exact location plus one of several messages:

  • "I'm here and OK."
  • "I need help."
  • "Call 911 and rescue me."

Several of our testers believe that a device like the SPOT unit would alleviate their family's worrying back home, making it easier for them to get permission to go on backcountry trips. This is especially true for solo walkers or people who pursue dangerous endeavors like technical mountaineering in areas beyond cell phone coverage. However, Backpacking Light makes no formal recommendations about what safety equipment any outdoor enthusiast should carry.

On paper, the SPOT unit is an innovative concept for improving backcountry safety. In the field, it did not deliver "virtually every message" as the SPOT unit's literature claims, and the unit has usability problems. As such, we believe it has yet to deliver its promised functionality and message delivery reliably.

What's Good

  • Provides vital last known location information and a time for that location.
  • Tracking mode automatically provides positional information every ten minutes.
  • Has three different message modes: OK (Check-in), Help, and 911.
  • Light and compact compared to many Personal Locator Beacons (PLBs) and with more message modes.
  • Long battery/operational life.
  • Low initial unit cost (but service fees are extra).
  • Help and 911 messages have a good probability of being delivered "with a perfect view of the entire sky."

What's Not So Good

  • The SPOT unit did not deliver "virtually every message." It is unclear what the SPOT unit's reliability rate of successfully delivering messages would be in the field conditions likely to be encountered backpacking and hiking (i.e. in conditions with less than a perfect view of the entire sky), and whether that reliability is sufficient.
  • No verification that a message was successfully delivered.
  • Confusing user interface.
  • User manual is short, lacking detail and closer to a quick start guide. It's also poorly organized and contains errors.
  • GPS receiver performance is not as good as the best handheld GPS units.
  • Tracking mode may have significant message gaps while hiking and backpacking.
  • Long wait time to transmit OK messages.
  • Website software has usability problems.
  • SPOT requires a service fee to work.
  • At 7.3 ounces (208 g) with batteries, the SPOT could be lighter.

Basic Specifications

These specifications have been summarized from the vendor specifications and our Testers' experiences.
  • The SPOT unit has four push buttons: Power-on, OK, Help, and 911. In addition, the Tracking mode is activated by a long press on the 'OK' button.
  • The SPOT unit has LEDs to show Power-on and the operation of the other buttons/modes. Various sequences and combinations of LED flashes are used to show the status of the unit and its operational mode.
  • Dimensions: 4.25 x 2.75 x 1.5 in (10.8 x 7.0 x 3.8 cm)
  • Weight: 7.3 oz (208 g), with batteries as measured by BPL
  • Battery Life: depends of type of batteries used. Using the two AA lithium batteries included with the unit, the manufacturer claims the following:
    • Power on, unused: approximately one year.
    • Tracking mode: approximately 14 days.
    • 911 mode: up to 7 consecutive days.
    • OK messages: up to 1900 messages.
  • Operating Temperatures: -40 °F to +185 °F (-40 °C to 85 °C)
  • Operating Altitude: -300 to +21,000 ft (-90 m to 6,400 m)
  • Floats in water and waterproof to 1 meter for up to 30 minutes
  • Shock: tolerates being dropped twice on all six sides from one meter onto hard surface.
  • Coverage: Much of North America, South America, Europe and Australia, Northern Africa and Northeastern Asia, and some distance offshore of these areas (see coverage map on SPOT website).
  • MSRP: $145.95 USD
  • SPOT charges a per-year fee of $99.00 US for basic service and the use of the system, which is in addition to the cost of the physical unit. The unit will not work without service activation.
  • Use of the Tracking mode is an additional $49.95 US/year above the basic service fee.

Review Objective and Testing

The SPOT unit manual claims "With a perfect view of the entire sky, the SPOT network is designed to successfully send virtually every message."

For a real world user, this may not be a useful claim. No one can plan their emergencies to happen with a "perfect view of the entire sky." Many (possibly most) places people routinely walk, hike, and backpack do not meet this requirement. There are usually mountains, hills, rocks, trees, canyon walls, or buildings blocking a portion of sky view. One's body blocks a significant portion of the sky view when just holding the SPOT unit. Short of putting the SPOT unit on a rock and walking away, there seems to be virtually no situation that meets the criteria of a perfect view of the entire sky when operating the unit. Finally, if you are in an emergency and/or injured, you may not be able to move to a location with optimal view of the entire sky.

Thus, our main review objective was to ascertain the SPOT unit's message transmission success rate for conditions likely to be encountered in the field by backpackers and hikers. A secondary objective was to determine the usability of the SPOT unit and supporting Web Software, as this ultimately affects successful message transmission. At the end of this review, we recommend a number of suggested improvements for the SPOT unit and the system that supports it.

To investigate the above, four Backpacking Light reviewers tested two SPOT units for more than three months. We tested on two continents and in both northern and southern hemispheres. Over the course of our controlled testing and field testing, we sent hundreds of messages.

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Field testing the SPOT in Australia.

Does the SPOT Unit Work?

No matter what the claimed potential of the SPOT system, the essential question is "Does the SPOT unit work?" Or more specifically phrased: "How reliably will the SPOT unit deliver messages and under what conditions?"

In our testing, in field conditions we believe likely to be encountered backpacking and hiking, the SPOT unit did not "deliver virtually every message," as the SPOT unit's literature claims. As such, we see the SPOT unit as an innovative system with a lot of promise, but with some glitches and room for improvement. We make no claims that the current SPOT unit and its supporting system is or is not dependable enough to deliver messages with sufficient reliability all times in the field conditions encountered by backpacker and hikers. That is a judgment call to be made by each prospective user.

SPOT Satellite Personal Tracker - Full Review - 3

SPOT Satellite Personal Tracker - Full Review - 4

Missing messages: (Left) A 4.5 mile section with only one of six expected SPOT messages. There should be five other messages between Track 1 and Track 3. (Right) Track log from a GPS unit (with an older technology GPS chipset) run in parallel with the SPOT unit during the field test. There was a clear sky view of the entire sky the entire time with no obstructions to satellite communication. (Basic image courtesy of SPOT & Google Maps)

The SPOT unit uses a very complex system to successfully deliver a message. Any single failure in this long, multi-component, multi-technology system path results in no message delivery. Some of the components (the Globalstar satellites, supporting satellite ground stations, the Internet, and email or SMS (phone) message systems) are substantially or entirely out of the SPOT unit's control. We found at least one instance of a system component downstream of the SPOT unit causing message losses in our testing. It is also possible that other unexplained long gaps with undelivered messages in our field testing might have been caused by a problem with a downstream component.

Initial glitches in new, complex systems like the SPOT are the norm, not the exception. In the future, SPOT may (or may not) fix many of these to significantly improve its performance from when we tested it and/or come out with a SPOT unit, Version 2. We asked John Dark of SPOT about improvements, and he said that, as a publicly traded company, SPOT could not commit to specific changes or time frames. SPOT's eventual success will be measured by

  1. Improvement in message delivery reliability.
  2. Improvements to the user interface and operation of the unit, including the user manual.
  3. Possible improvements to components downstream in the communication chain that the physical SPOT relies on for successful message delivery.

As a result of our testing, we make a number of recommendations for the current SPOT unit, as well as ones for a potential Version 2 of the physical SPOT unit, which could bring it closer to the performance and functionality of the manufacturer's claims and the field reliability expectations for backpackers and hikers. These recommendations are covered at the end of this Review.

For those interested in our technical testing information, it is summarized in an Appendix. In most cases, the individual citations in the Appendix are a few examples that represent a larger number of similar tests as well as our field tester's experiences.

Basic Operation of the SPOT Unit

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A diagram of the major elements in the SPOT communications chain. (image courtesy of SPOT)

When the SPOT unit is activated, the following steps take place:

  1. The unit attempts to obtain a GPS position from the standard GPS satellite system.
  2. The unit then transmits the required message (OK, Tracking, Help or 911) up to an orbiting Globalstar satellite on the Simplex data channel.
  3. The Globalstar satellite relays this message down to the nearest Globalstar ground station.
  4. The ground station then transmits this message to the SPOT head office.
  5. The SPOT head office adds some extra information to the message and
    • posts it on its own website and/or
    • sends the message to up to ten nominated recipients by email and/or SMS (phone text) or
    • in the case of a 911 message, contacts the Globalstar office (GEOS Emergency Response Center), where a human operator takes over to contact the appropriate emergency services.

Some further explanation:

  • When 'OK' is pressed, the SPOT unit attempts to obtain a GPS fix and will not transmit until it has done so. If and when it does get a fix, it then transmits the same message and GPS position three times over what remains of twenty minutes from the press. If more than one of the attempted messages is received, only the first one is logged and emailed per step 5 above.
  • In principle, the green LED above the 'OK' button should tell the user what is going on - whether a GPS fix has been obtained and when a message is being sent - but all testers found this form of feedback confusing.
  • When 'Help' is pressed, the SPOT unit will attempt to get a GPS fix for a short duration, then will transmit a 'Help' message. If it has a GPS fix, the coordinates are included in the message; if it did not get a GPS fix, the message is sent without the GPS coordinates. The 'Help' message is then retransmitted every five minutes for one hour or until the function is cancelled. Every one of these messages is handled according to step 5 above (none are discarded). The function can be cancelled with a long press of the 'Help' button.
  • When '911' is pressed, the same sequence as for "Help" is followed, but with a '911' message instead of 'Help'. This message is repeated every five minutes until the batteries are exhausted or the function is cancelled. These '911' messages are handled differently from the 'Help' messages: they stop at the Globalstar office, where a human operator takes over to contact the appropriate emergency services in the appropriate country.
  • The owner of the SPOT unit can define a short text attachment to a 'Help' message, to be sent via the SPOT website. This requires access to SPOT's website, thus it cannot be changed once you are in the field.
  • OK messages have an identical text attachment feature.
  • Information added by SPOT to the basic messages sent out in step 5 includes a URL to the relevant Google map with the GPS location marked on it - a very useful feature.
  • When the 'OK' button is pressed for more than five seconds, the SPOT goes into Tracking (also called 'SPOTcasting') mode. In this mode, the SPOT unit attempts to get and transmit a GPS reading every ten minutes. This creates a 'breadcrumb' trail which can be displayed on a Google map at the SPOT website.
  • The Tracking mode messages are not sent via email. They can only be accessed by logging onto the SPOT website with a username/password. (SPOT may soon have a way to publicly share Tracking points with friends and/or emergency contacts, if you wish to do so.)

Search and Rescue Perspective

Ron Johnson, Grand Teton National Park Search and Rescue (SAR) team member, says that "the SPOT provides a vital piece of SAR information, the last known location of the party and the time at that location." This limits the search area, making the SAR team faster and far more effective than if they had "just the information that they left X trailhead four days ago." Ron notes even when talking to lost parties via cell or satellite phone, some have been unable to describe their location well enough for SAR teams to know their exact position.

Ron views the SPOT unit's Tracking mode as possibly the most useful, since it updates the "last known location" every ten minutes without the user doing anything. We note that you must physically activate Help or 911 modes after an emergency. If you can't (you are too injured in a fall, for example), nobody knows there is a problem. However, with Tracking mode active, even if you are suddenly injured, rendered unconscious, or are too incapacitated to activate a Help or 911 message, your emergency contact monitoring the SPOT website will still have your precise last known location from Tracking messages. They will eventually notice your lack of movement as a sign of trouble. The need for last known position also indicates judicious use of the SPOT unit's OK (Check-in) mode to provide position information.

According to Ron, the downsides of the SPOT unit from a SAR perspective are that "you do not know the nature of the emergency," and "you cannot talk to the party requesting help." In the first instance he says, "A well constructed short sentence or even 'injured - unable to move' means a lot to SAR folks" (A simple field-configurable text message to accompany a Help message is one of our recommended improvements for the SPOT.). In the second instance, where there is a cell or satellite phone contact, he says, "we've been able to talk people onto the right route or give medical advice for an injured party member. Many times [there is no real emergency and] we've advised the party to make themselves comfortable and sit tight until morning. Sometimes all they need to hear is an experienced voice to tell them it's going to be OK [and to keep them from panicking and doing something rash, which could cause a problem]."

Analysis of Test Results

Antenna Design

The SPOT unit receives signals from GPS satellites on one frequency and transmits messages to communications satellites on another frequency. It uses the same antenna to do both. One antenna cannot be optimized for two frequencies. If it works better for one frequency (message transmission) then it will not work as well for the other frequency (GPS location reception) or vice versa.

We asked John Dark, Senior Marketing Manager for SPOT, about the shared antenna design. He said their design favors message transmission. They picked favoring transmission because they believe getting an emergency message out is the highest priority. Even without a GPS position, a Help or 911 message is still of great value.

The choice of a single antenna that favors message transmission may be why the SPOT unit does not have the same GPS fix performance of a handheld GPS unit using a similarly sensitive GPS chipset (The GPS-only unit presumably has an antenna optimized solely for best GPS reception.).

A reduction in GPS performance has problematic implications. First, as Ron Johnson noted above, the last known location of the party is a vital piece of information for SAR personnel. Second, two modes of the SPOT unit, OK and Tracking, require a GPS fix or they will not transmit. Lack of GPS reception is one possible contributor for the OK and Tracking modes to have lower successful message delivery rates than Help messages, which do not require a GPS fix.

One of our recommendations for improving the SPOT unit is to use two dedicated antennas, one optimized for receiving GPS signals and another for transmitting messages.

Obtaining a GPS Fix

We found that the SPOT unit could not match the GPS reception performance of the best current generation handheld GPS units. Heavy tree cover and other obstructions that limit sky view challenge most GPS units, but recent high sensitivity GPS chipsets have decreased this problem.

To see how the SPOT unit does with a limited sky view, we tested GPS performance under an overhang with two Garmin GPS units and the SPOT unit. At two positions, the SPOT unit failed to get a GPS fix while the latest version of the Garmin H series GPS acquired a fix in both positions. An early generation technology Garmin unit was comparable in performance to the SPOT unit.

We also field tested the SPOT unit under heavy tree cover. In this case, a substantially older technology Garmin unit appeared to outperform the SPOT unit. (Note that we are comparing GPS track points to the SPOT unit's delivered messages, so this is not an exact comparison.)

The SPOT instructions recommend using the SPOT unit horizontally (face up). We found that tilting the SPOT unit sideways significantly reduced GPS performance. When the SPOT unit is stuffed into a pack, some degree of tilt is almost inevitable, though we found that tilt of less than forty-five degrees would not significantly affect GPS performance. From our testing, we also found that the ninety degree angle (from horizontal) created by hanging the SPOT from its belt clip reduced successful message transmission rates in Tracking mode.

Nearby cliffs and boulders can cause reflections of the signals transmitted from the GPS satellite, which can make the apparent position to be in error by a kilometer or more (We experienced with a nearby cliff in one field test.). However, it seems the SPOT unit is more prone to problems here than some other GPS units, such as a Garmin H series unit.

Tracking Mode When Backpacking or Hiking

We found Tracking mode when backpacking or hiking had low message delivery rates. Antenna design and GPS performance may be factors, since Tracking messages are not transmitted without a GPS fix. It is difficult to mount or hold the SPOT unit in a way that your body (especially torso) doesn't block a good portion of the sky view. Block some sky view, and you affect GPS reception.

Four of our testers evaluated successful message delivery rates while walking with the SPOT in Tracking mode. They typically put the SPOT face up in a fanny pack or horizontally on the top of a backpack, hip mounted it as the SPOT Manual suggests, or held the unit in front of them. Each went for a one hour or longer walk in Tracking mode. In two cases, no messages were successfully delivered during the entire walk. In another, a single message was received in the entire hour. Careful inspection of the coordinates showed it had been transmitted when the walker stopped (at a known location) to re-lace a shoe. In several cases, the SPOT unit was placed face up on a rock under a clear sky for some time immediately after the walker returned home, and in each case, most of the messages from this stationary position were received.

Two possible contributors to undelivered messages would be reduced GPS performance due to movement of the SPOT unit or limited sky view for the SPOT unit when it was close to the hiker's body (the body blocks sky view). From our testing on a moving kayak, which had higher message transmission rates than walking, it is probable that close proximity to the hiker's body is the greater contributor, but we cannot completely rule out movement as a secondary contributor. There may even be other factors at play to prevent message delivery.

We asked John Dark of SPOT about our undelivered Tracking messages. He said that other users had reported undelivered Tracking messages as well. For best use of Tracking mode, he suggested "mounting the SPOT unit horizontally on the top of a pack shoulder strap. In this way, only your head blocks a portion of the sky." (Note: the User Manual instructs a vertical mounting at your waist using the SPOT unit's belt clip.)

We agree that the top of the shoulder strap mounting would probably improve Tracking message delivery, as no portion of your torso would block sky view. However, even with a perfect view of the entire sky, our testing indicated average daily Tracking message delivery rates of 83%, with some rates as low as 17% in a given one hour period.

Message Reliability

In various controlled tests and our field testing, we found that somewhere between 0% and 83% of messages were successfully delivered, depending on the amount of sky visible to the SPOT unit and the mode used. This is a broad range. In addition, difficulties with SPOT unit's user interface meant that incorrect modes were sometimes activated, which resulted in unsent messages. These unsent messages were not counted in our reliability figures, but nevertheless may affect users' real world reliability.

SPOT recognizes that not all messages will be delivered, and addresses this by sending multiple messages. A single OK message is transmitted up to three times in twenty minutes. A Help message is transmitted once every five minutes for an hour. A 911 message is transmitted every five minutes until the batteries give out.

Our testing suggested that Help and 911 messages would have a high probability of being delivered "with a perfect view of the entire sky" when in SPOT's high coverage areas. OK and Tracking messages would have a good but lesser probability of successful delivery "with a perfect view of the entire sky."

It is unclear what the SPOT unit's reliability of successfully delivering messages (four types) would be in field conditions likely to be encountered backpacking and hiking (conditions with less than a perfect view of the entire sky), and if that reliability would be sufficient.

No Message Delivery Confirmation

Another wrinkle to the possibility of an undelivered message(s) is that the SPOT unit cannot confirm successful message delivery. The SPOT unit sends to communications satellites, but cannot receive from the satellites. Thus, there is no way to send a message delivery confirmation back to the SPOT unit.

Suppose a hiker has severely sprained an ankle or broken a leg in an area of heavy tree cover or in a deep canyon with limited sky view. Should they assume a Help or 911 message was successfully delivered and with a good GPS location? If so, they should probably sit tight and wait for rescue. Or should they assume a low probability of message delivery (and/or the lack of GPS location) and hobble as best they can towards some place where they can get help or at least have a higher chance of being discovered?

If our hiker decided to stay put, but the SPOT unit's message was not delivered (or lacked a GPS location), they could be in for a long, cold, and hungry wait. If they decide to hobble to a better location, and the message was delivered, they may unnecessarily cause far a more serious injury to themselves, and they will not be in the location of their Help or 911 messages, where SAR will look first. The range of problematic scenarios in this vein is worth consideration.

SPOT Website

Most of the testers had some initial problems with the SPOT website. Its design is not particularly intuitive, and there are some features we'd like added. However, the problems were minor, and from our Conversations with John Dark of SPOT, we expect improvements to their website in the near future.

SPOT email messages include a location URL. Click on the URL and up pops a Google map with the position marked. This makes it very easy for people monitoring your trip to see where you are. While they are not emailed, Tracking messages are viewable on the SPOT website. If you select a series of logged Tracking positions, you can display a map of the region with position tags at all the logged message locations (see the Technical Appendix for a screenshot of this feature).

SPOT User Interface

The SPOT unit has only four buttons and four LEDs. It should be simple to use. In practice, we found it confusing to activate, cancel, and inactivate all the SPOT functions. Different modes are activated by long or short presses of the same button. Some modes stop by themselves, some can be cancelled by button presses, and others can only be stopped by turning the unit off. We believe that most users would need a field crib sheet to remember all the operations. We also found the few LEDs and their cryptic combinations of flashes did not provide enough feedback on what the SPOT unit was or was not doing, even if one had nothing to do but stare at the LEDs, which is usually not the case in the field. The attempt to transmit a message is indicated by the LEDs going solid for two seconds. Blink and you'll miss whether the SPOT transmitted a message or not. The SPOT does not keep track of attempted message transmission. Once that information is gone, it's gone.

A usability example: Pressing the 'OK' button normally causes the SPOT unit to send up to three OK messages with the same GPS coordinates. Pressing it for more than five seconds puts it into the Tracking mode, which sends one message every ten minutes until you turn it off. The status flash sequence is the same for both modes, so you have no idea which mode is active.

One tester was using Tracking mode while on a sea kayaking trip (see Appendix), and had notified friends back home that he would do this. However, one morning in bad weather prior to a hazardous section of the trip, he accidentally released the 'OK' button a shade too soon, and the SPOT went into OK mode instead. One OK message was sent, and nothing more for the rest of the section. His friends knew this portion of the trip was exceptionally hazardous: imagine their dilemma when they only got one OK message instead of the series of Tracking points they were expecting. Had the kayak foundered and sunk in the bad weather, or had the kayakers just decided to stay put and wait for safer conditions? What to do?

The problem is that the feedback provided by the current SPOT design consists of a few flashes of the LEDs. In many situations it's not feasible to sit and focus on the SPOT LEDs for up to twenty minutes to find out what the SPOT is doing, if it has a GPS fix, and if a message was sent. Look away briefly and you might miss an important LED flash. Was a message sent or not? If it was sent, what type of message? What mode is the SPOT in? This may not be the best design for an emergency/safety system.

John Dark of SPOT told us that other users have reported inadvertently activating OK when they intended to activate Tracking. SPOT intends to re-write the manual to look for a solid LED light indication that Tracking has been activated, rather than waiting a potentially ambiguous five seconds. This rewrite will still not change the same status flash sequence that OK and Tracking modes share.

Enhanced SPOT Display

All our Testers noted that the SPOT unit had the current GPS coordinates inside but could not display them. Many problem situations are little more than "Where are we?" Displaying your position on the SPOT unit could possibly eliminate the need to carry a separate GPS unit. As noted earlier, the four LEDs convey very little information about the operation of the SPOT unit. May times we wished for an improved display for feedback on the current SPOT mode, the quality of the GPS fix, and number of attempted message deliveries, etc. A more sophisticated LCD text display is the obvious solution to these needs, though it would decrease the impressive battery life.

SPOT Versus Other Options

Personal Locator Beacons

The PLB system is an obvious alternative to the SPOT. The older PLB system, now being phased out, simply transmitted a beacon for the authorities to home in on. The newer PLB system (on 406 MHz) does more than that: the units can also contain a GPS unit and can transmit the GPS coordinates. In effect, this makes the newer 406 MHz PLBs equivalent to the SPOT with only the '911' button.

The new PLB system may have several advantages over the SPOT:

  • Many planes are equipped to detect the PLB signals, and there are two global satellite systems, called GEOSAR and LEOSAR, which specifically monitor the 406 MHz frequency for distress signals. This combination might be more reliable than the Globalstar system.
  • The PLB unit contains the 406 MHz transmitter for the satellites and a lower frequency beacon at 121 MHz, which serves as a homing frequency for search organizations, some of which have gear which can locate this beacon.
  • There is no annual service fee for the use of the PLB system: it is taxpayer-funded.
  • Typically, a PLB will have separate antennae for the GPS and the transmitters. This may make the GPS sensitivity in a PLB higher than in the SPOT unit, which has a single antenna (although there are many other sensitivity factors as well).
  • If the GPS coordinates are not available, the PLB system still locates the unit using timing variations as detected by the satellites. At close range during an actual search, the homing beacon helps to locate the unit.

However, a PLB is usually more expensive than the SPOT unit and can only send a non-text Emergency/911 message, while the SPOT can send three other message types. Both the SPOT unit and the 406 MHz PLBs are new. Which one would prove more reliable at bringing in a search party may not be known until statistics are compiled on the success rates of notifying emergency personnel.

Satellite Phones

As noted earlier by Ron Johnson, there are significant advantages for phone communications in an emergency (over the SPOT or PLBs).

If the SPOT can reach a satellite, so can a satellite phone - they have similar (if not exact) areas of coverage. In many ways, a satellite phone would be the ultimate solution, but for two things: they are currently heavy, an almost inevitable consequence of the need for a bigger antenna and bigger batteries, and they are expensive and the service costs are high. Should satellite phones come remotely close to the cost of ordinary mobile or cell phones, this option would likely surge in popularity among backcountry users.

Cell Phones

Cell phones would be a great option, if they had full coverage of the backcountry wilderness areas. For this to work, the backcountry would have to be covered by a grid of cell phone towers and other supporting infrastructure. This is not likely to occur in the foreseeable future.

However, places like Mt. Rainier and the Tetons have decent cell phone coverage for many areas, provided you are high enough. Ron Johnson told us of numerous SAR contacts by climbers, hikers, and backpackers via cell phone in the Grand Teton National Park. In many other "backcountry areas," you can get intermittent to good cell phone coverage from high ridges and peaks. Some of our testers have had better luck transmitting a single SMS text message in fringe cell phone coverage.


So what is the SPOT unit's reliability to successfully deliver messages? To better understand our findings, we break this question into separate sections and a final statement.

Reliability with a Perfect View of the Entire Sky*

With a perfect view of the entire sky, our six day kayaking field test produced daily successful message delivery rates of 75% to 83%. This success rate dropped to as low as 50% for a given two hour period and 17% for a given one hour period. The longest gap without successful message delivery was forty minutes. These message delivery success rates were for individual message transmissions sent out at ten minute intervals with the SPOT unit in Tracking mode. As such, it is a direct measure of the Tracking mode's successful message delivery reliability with a perfect view of the entire sky, or "ideal conditions."

In our six day field test, all attempted OK messages, sent morning and evening, were successfully delivered. It should also be noted that two scheduled morning OK transmissions were not sent. Due to dangerous conditions, our testers could not afford to wait twenty minutes for an OK message transmission and instead initiated Tracking mode and got underway. The lack of an OK message caused concern for our field tester's emergency contact monitoring SPOT messages. In this case, the multiple message/long wait period for the OK mode was a disadvantage.

From our field testing, we estimate that with a perfect view of the entire sky, Help and 911 messages have an excellent probability of getting through. Both modes send multiple messages frequently and for a long period (one hour for Help, and until the batteries fail for 911). In our six day kayaking field test with perfect sky view of the entire sky, we had no message delivery gaps lasting an hour or longer.

An OK message would also have a good chance of getting though with perfect view of the entire sky, but not quite as good as Help or 911. After initiating OK mode, the SPOT unit makes three attempts to send a message in whatever is left of the twenty minutes after the SPOT unit gets a GPS fix. During our six day field test, we had twenty-eight periods of approximately twenty to forty minutes with no successful message delivery. If we had initiated an OK mode during those periods, the message might not have been delivered. In our controlled testing, we had instances where OK messages were not delivered. We also had a number of instances where the OK message was delivered in the last attempt of the twenty minute period, indicating that SPOT had difficulty with first two attempts.

Also decreasing the probability of sending an OK (or Tracking) message is the requirement that SPOT have a GPS fix before attempting to send a message. With no GPS fix, no OK or Tracking messages are sent (Help and 911 modes do not require a GPS fix to send), and our testing indicated that while good, the SPOT unit's GPS performance falls short of the best handheld GPS units currently on the market.

In summary, with a perfect view of the entire sky, Help and 911 messages have an excellent probability of successful delivery (although with a slight possibility of lacking location information due to GPS reception performance). OK messages have good but lesser probability of successful delivery, and Tracking messages have approximately an 80% probability of successful delivery during the course of the day, though this can drop as low as 17% for a two hour period.

Again, these rates probably do not apply to more limited sky view situations, including those with the SPOT close to your body, nor do they apply to areas with hills, trees, canyons, or other situations normally encountered backpacking and hiking (more below).

It seems reasonable to assume that many people cannot plan all their emergencies to happen with a perfect view of the entire sky. It is unclear what the SPOT unit's reliability of delivering messages would be in field conditions likely to be encountered backpacking and hiking - that is, with mountains, hills, trees, narrow canyon walls, or even your body blocking most or part of the "perfect view of the entire sky."

Reliability with Less Than a Perfect View of the Entire Sky

SPOT gives no message reliability rates for situations with less than a perfect view of the entire sky, nor do they guarantee that a message will get through with less than a perfect view of the entire sky. John Dark of SPOT mentions making multiple message transmissions as a way of improving the chances that one message will be delivered in areas with less than a perfect view of the entire sky. He said the longer you wait, the better your chances that a satellite will be overhead to receive a transmission. However, in our field tests and controlled tests, we found instances where the SPOT was unable to get a message out no matter the number of attempts. As expected, most of these situations occurred where the SPOT had less than a perfect view of the entire sky (for now "limited sky view"). Because it does not rely on a GPS fix, we found fewer situations where a Help message was not sent, but we do have examples of Help messages sent without a GPS position.

Many of these limited sky view situations are ones that would be routinely encountered hiking or backpacking. Heavy, but not complete, tree cover is just one example were the SPOT was unable to successfully deliver most, if any, messages. As mentioned earlier, many people can't plan on having emergencies only in areas with a perfect view of the entire sky.

SPOT Satellite Personal Tracker - Full Review - 6

SPOT Satellite Personal Tracker - Full Review - 7

Undelivered messages with trees: (Left) We expected five SPOT messages between point A to point B but the SPOT only sent one Tracking message (at point C) in the three mile long tree lined creek. We believe it only managed to transmit at point C due to a widening in the creek indicated by the X arrow. (Right) Track log from a GPS unit (with an older technology GPS chipset) run in parallel with the SPOT during the field test. (Basic image courtesy of SPOT & Google Maps)

We asked SPOT for some guidelines for when a user could expect a successful message delivery. John Dark replied that the number of field variables that could affect message delivery is far too complex to even come close to a simple list. He suggested that since they believe transmitting is more successful than GPS reception, one might use "having a GPS fix" as an indicator of a higher probability of successfully delivering a message. While this may help, it is not conclusive. It also does not address the need to make a pre-trip assessment of whether you'll be in areas where the SPOT might not successfully deliver messages.

Reliability in Tracking Mode when Hiking or Backpacking

When hiking or backpacking, a significant portion of the SPOT unit's sky view is usually blocked by your body. This may be a cause for lower message delivery rates when hiking or backpacking in Tracking mode versus kayaking, where the tester's bodies did not block the sky view. We had multiple hikes with message delivery rates of 17% or lower for the whole hike. We had least two instances of an hour or longer hike where no messages got through. We tried mounting the SPOT horizontally on a fanny pack, clipped to the hip as SPOT suggests, and handheld, all with similar results. John Dark of SPOT suggested mounting the SPOT horizontally on the top of a shoulder strap. While this may help (this advice was received after field testing was completed), we would not expect it to do any better than the message delivery rates from the kayaking test. With a less-than-perfect view of the entire sky, we would expect lower message delivery rates.

SPOT's Caveat - "Based on Network Availability"

SPOT reliability claims on their coverage map carry the caveat "based on network availability." At first glance, we interpreted this to be a wiggle room statement. That is, even with a perfect view of the entire sky you might not get SPOT's claimed 99% message delivery for their best coverage areas. As an example, one of our reviewers could not get messages delivered, even though SPOT claims 99% message delivery reliability in his coverage area. He contacted SPOT, and they informed him a ground station was undergoing maintenance for a couple of days.

John Dark says "based on network availability" is statement recommended by SPOT legal council. It is intended to convey that the 99% figured is based on measured statistics on the satellite communication system supporting SPOT. We found this ambiguous and confusing. Our best guess is that it means "99%" may not be based on long term measurement of message statistics of successful message delivery from an actual SPOT UNIT. As such, the claimed "99% message delivery" is more likely a prediction of what message delivery might be, and is not a statistic based on direct measurement of successful message delivery rates (starting with pressing a button on the SPOT unit and ending with the successful message delivery to a final recipient). Whatever "based on network availability" actually means, it seems clear that SPOT is not legally obligating itself to meet this 99% message delivery rate to SPOT unit users.

Finally, we leave it to the reader's personal experience to assess the chances of email and SMS phone text systems successfully delivering messages, or even the possibility that an "OK" or "Help" message might end up in a SPAM folder.

All this emphasizes that one is relying not only on the physical SPOT unit, but a long chain of other systems in "the network," the Globalstar satellites, supporting satellite ground stations, SPOT's website and message center, the Internet, and email or SMS (phone) text message systems. It is entirely possible that significant periods of unsent messages in our kayak field testing could be from a failure somewhere downstream in the network chain after the SPOT unit successfully sent messages.

User Interface

We had one instance where the SPOT unit's user interface contributed to a failure to transmit messages during the riskiest section of travel in one our field tests - the time during the trip when our field testers most needed to get messages out.

All our testers found the SPOT's user interface non-intuitive. The same button operates different modes, depending on how long it is pressed. The blinking LEDs are hard to interpret, but even when fully understood, they still do not provide enough information about the SPOT unit's status and operation. One must watch the blinking LEDs continually to see if the SPOT unit attempts to transmit a message. If you blink or look away, you may miss the two second period when the LEDs are solid, indicating a message is being transmitted. The SPOT does not retain information on what messages were transmitted, or even if they were transmitted at all. Also, and more serious, there is no way to determine if a transmitted message was successfully delivered.

In the End, It's a Personal Decision

We neither encourage nor discourage using the SPOT unit. No system is 100% reliable in all conditions. No piece of equipment is appropriate for all situations. On paper, the SPOT unit is clearly an innovative backcountry safety product. The question remains: Does SPOT deliver messages with sufficient reliability - not just for a "perfect view of the entire sky," but with sufficient reliability for conditions likely to be encountered in the field when backpacking or hiking?

We are aware that there may be some positive reviews and significant endorsements for the SPOT. We ask the reader to ascertain if these are based solely on unverified SPOT performance claims or whether they provide a body of test data to substantiate those positive opinions.

In the end it is up to each potential SPOT user to determine

  • their communications needs,
  • the level risk they are comfortable with,
  • what message delivery reliability they deem acceptable,
  • and under what conditions they expected to transmit messages.

We hope that that our readers will use all available information - this review, other publication's reviews, SPOT's literature, and any other materials - to make their best decision.

Be safe out there!

The Backpacking Light SPOT Review Team

Recommendations for Improvements

Improvements that can be easily made to the current SPOT:

  • Rewrite the SPOT User Manual in more detail with significantly more consultation with people who have field experience using the SPOT unit.
  • Include a small waterproof instruction card no larger than the SPOT unit. If possible, this should be attached to the SPOT unit.
  • Allow longer messages and more message recipients on the SPOT website.
  • Add an option of including UTM coordinate position in SPOT email messages.
  • Allow Tracking messages to be emailed in addition to being tracked on the website.
  • Make the SPOT website more intuitive.

Improvements that would require a physical change:

  • Improve SPOT GPS performance. This could be done by a separate GPS reception optimized antenna, a better GPS chipset, improved processing, or possibly all three.
  • Devise some system whereby carrying the SPOT while hiking or backpacking does not significantly interfere with Tracking mode. This may require the use of two antennae as in the previous point. Ideally, the SPOT, or possibly an external antenna(s), would be horizontal and away from your body.
  • Improve message transmission reliability in difficult conditions.
  • Add an alphanumeric or graphic display to relay operational status to the user and as a menu for initiating and cancelling modes.
  • Provide a rudimentary GPS coordinate display.
  • Significantly reduce the weight of the SPOT unit - mobile phones with embedded GPS receivers weigh a fraction of what the SPOT unit weighs.

Satellite communication changes:

  • Switch the SPOT to a duplex satellite channel and provide "message received" acknowledgement to a user.
  • A more radical suggestion is to allow the SPOT unit to send a brief text message composed in the field. One could send critical information about a medical emergency this way, bringing the SPOT unit closer to the functionality of a satellite phone by providing critical information to SAR personnel.

Technical Appendix

Here we briefly outline some of the testing done during the review process. Testing was performed both in a laboratory environment and in the field.

Six Day Extended Field Test with a Perfect View of the Entire Sky

Numerous tests under different field conditions with less than a perfect view of the entire sky showed our testing team that message delivery could be as low as a 17% success rate (even lower with heavy tree cover or other significant obstructions limiting sky view).

We decided to run a full-scale field test over six days to give the SPOT unit a perfect view of the entire sky almost the entire time. We used a sea kayaking trip near the Gulf of Mexico to do this. In this field test, the SPOT unit was mounted face up on the deck of a kayak away from people so that not even our bodies blocked a significant portion of a perfect sky view. The unit was horizontal the whole time, ensuring optimal antenna position. We traveled almost entirely on large bodies of water, where there were no trees, hills, or other objects blocking the SPOT unit's sky view. We believe this best approximated SPOT's "perfect view of the entire sky." As such, the successful message delivery rates in this test would probably not apply to hiking or backpacking where a number of natural features (or even the hiker's body) can block a significant portion of the sky view.

On the trip, we used a combination of morning and evening OK messages and activated Tracking mode for the rest of the time we were traveling.

SPOT Satellite Personal Tracker - Full Review - 8

SPOT Satellite Personal Tracker - Full Review - 9

Two out of every ten messages did not get through: Although there are a few obvious large transmission gaps (indicated with a yellow arrows), transmission appears generally good for the trip. However, even in what appear to be the consistent transmission sections there are smaller and even moderate sized gaps (white arrow). (Basic image courtesy of SPOT & Google Maps)

With a Perfect View of the Entire Sky

While the SPOT unit had some problems in these almost ideal conditions, it performed much more closely to the manufacturer's claims than in any other conditions we tested. There were still message delays, long periods with tracking gaps, and only one transmission in a tree-lined section of the route (there was a brief section where sky view was less impeded).

Some of these gaps are marked by the yellow arrows in the map here. The SPOT unit also suffered from usability issues. Our OK messages were not sent on some mornings, due to the long wait time while the SPOT unit tried to get a GPS fix.

It should be noted that while the examples shown here are taken from a six day trip, they were not brief, isolated incidents. Data from other excursions and controlled testing is consistent with the message delivery success rates shown here.

Transmission Reliability Statistics from a Six Day Field Test

Entire Trip

Number of Possible Track Messages 222
Number of Track Messages Sent 186
Number of Track Messages Unsent 36
Percentage Sent 83.8%*
*Note: Percentage Sent drops below 80% if you include twelve missing tracks over a two hour period due to poor usability (we did not realize Tracking wasn't on).

Worst Day (Open Sky)

Number of Possible Track messages 40
Number of Track Messages Sent 30
Number of Track Messages Unsent 10
Percentage Sent 75.0%

Worst Two Hour Period (Open Sky)

Number of Possible Track Messages 12
Number of Track Messages Sent 6
Number of Track Messages Unsent 6
Percentage Sent 50.0%*
*Note: The SPOT unit had 53.3% sent in two other two-hour periods.

Worst One Hour Period (Open Sky)

Number of Possible Track messages 6
Number of Track Messages Sent 1
Number of Track Messages Unsent 5
Percentage Sent 16.7%  

Worst One Hour Period (With Trees)

Number of Possible Track Messages 6
Number of Track Messages Sent 1
Number of Track Messages Unsent 5
Percentage Sent 16.7%*
*Note: The single message sent was in a wide (easier transmission) area.

With Less than a Perfect View of the Entire Sky

SPOT Satellite Personal Tracker - Full Review - 10

SPOT Satellite Personal Tracker - Full Review - 11

Undelivered messages with trees: (Left) We expected six SPOT messages between point A to point B but the SPOT unit only sent one Tracking message (at point C) in the three mile long tree lined creek. We believe it only managed to transmit at point C due to a widening in the creek indicated by the X arrow. (Right) Track log from a GPS unit (with an older technology GPS chipset) run in parallel with the SPOT UNIT during the field test. (Basic image courtesy of SPOT & Google Maps)

SPOT Satellite Personal Tracker - Full Review - 12
With more detail one can see that the SPOT unit probably gained GPS reception at the widening starting at point X and then managed to transmit position at point C, another very wide section. Without this 0.2 mile wide stretch, we believe the SPOT unit would not have sent a single message on the creek. (Basic image courtesy of SPOT & Google Maps)

A portion of this trip was along a tree-lined creek. It was the only portion of the trip with significantly limited sky view. The sky above was visible, and you can clearly see the creek in the satellite imagery. However, the sky view was narrow due to the width of the creek and the height of the trees. The SPOT unit managed only one tracking message in the three miles shown here, and it only managed that tracking point at wider section of the creek about halfway through, starting at X and sending at C. The widening here approached an open sky view that was sufficient for the SPOT unit to get a GPS fix - the precursor to transmitting a Tracking message. Without that widening, the SPOT unit would possibly not have sent a single message along the creek. In contrast, a Garmin GPS Map 76C (using an older technology GPS chipset) maintained a GPS fix the full distance of the creek.

References have been made to the problems of distinguishing between the OK mode and the Tracking mode and how easy it is to activate an OK message when intending to activate Tracking mode. This happened one morning while launching off an unprotected beach on the Gulf of Mexico. Winds were already at twenty knots and forecast to increase to thirty-plus knot headwinds in the next hour. A 5.5 mile open water crossing in three-foot seas was required, with higher seas over numerous shoals. The wind was blowing away from land and threatened to blow the kayaks into the Gulf. Because it had been dangerous boating conditions for days, there were no boats on the Gulf, and rescue was unlikely in case of trouble. This seemed like an ideal time for the Tracking mode.

Under the stress of getting off the beach in high winds and rough surf, the OK button was not pressed long enough to get into Tracking mode. Instead, a single "OK" message was sent at the start, and nothing more was sent for the rest of the dangerous crossing. Due the poor design of the SPOT unit's LED display, this mistake was not discovered until the full crossing to a sheltered creek mouth was complete. Fortunately, the emergency contact back home did not panic when no Tracking messages were received.

If it was that easy to make a mistake when in a moderate stress, non-life threatening, non-emergency situation, one wonders how much higher the probability of making a mistake would be in a true emergency.

Limited Sky View Test

SPOT Satellite Personal Tracker - Full Review - 13
The SPOT unit was frequently unable to acquire a GPS fix (or send messages) with limited sky view. A high sensitivity GPS had no difficulty obtaining a fix, even with severely limited sky view. With somewhat limited sky view, the SPOT unit struggled to send a message out in twenty minutes. Only in the easiest test did the SPOT unit manage to quickly send a message out within one minute.

We know that all GPS systems need some view of the sky and that transmission to a satellite also requires some view of the sky. This was tested by placing the SPOT unit, a recent Garmin HCx, and an older Garmin Cx unit side by side, a variable distance under an overhang. The units started at a position deepest under the overhang where their view of the sky was most limited (hardest position) and were then moved forwards at intervals (progressively more sky view) until the SPOT unit could quickly get a GPS fix and send an OK message (easiest position with most sky view).

Four distances were tested. The SPOT unit was unable to get a GPS fix or send a message in the first two positions (severely and very limited sky views, respectively). The Garmin HCx unit easily got a GPS fix at these two positions. At the third position, under somewhat limited sky view, the SPOT unit gained a GPS fix in under five minutes. It successfully sent a message in its last attempt at twenty minutes.

Our best guess is that the SPOT unit had a tenuous GPS fix at the third position, and that it also had some difficulty in transmitting a message to the GEOS communications satellites that was successfully delivered. At this position, the Garmin Cx also had a shaky GPS fix that occasionally dropped out. Only in the last and easiest position, with only slightly limited obstruction of sky view, did the SPOT unit quickly get a GPS fix and send a message in approximately one to two minutes.

This suggests that the SPOT unit's GPS performance is on a par with the older generation Garmin Cx series, but not as good as the high performance Garmin H series, which quickly obtained a fix at the hardest position. (Later in our six day field test, a much older receiver technology unit, a Garmin GPSMap 76C GPS, appeared to outperform the SPOT unit on a tree-lined creek. See below).

Unfortunately, while most dedicated GPS receivers display the quality of a GPS fix, the number of satellites connected, and the relative signal strength, as well as positional accuracy, the SPOT unit has no provisions to do so. Therefore, the user may not be aware of when the SPOT unit is having GPS reception problems in a fringe reception area where the signal is shaky and dropping in and out. The SPOT unit only has two LEDs blink out of sequence when it does not have a GPS fix, and they only do so after five minutes. For the first five minutes, they blink in sequence whether they have a fix or not.

Field Test - Tracking Mode While Walking

SPOT Satellite Personal Tracker - Full Review - 14
One Tracking Mode test under good conditions, with SPOT placed horizontally in a bum bag.

The red block indicates the time frame in which Tracking was enabled.
A solid pink box indicates where a message was received on schedule.
A hollow pink box indicates where a message should have been received, but was not.

The SPOT unit was put into Tracking mode, placed face up in a bum-bag (fanny pack), and taken for a one hour walk (8:20 to 9:20). Messages should have been received every ten minutes. The only message received in the first hour was transmitted when the walker stopped to re-lace a shoe (8:30). We know this from inspecting the exact position on the Google map. The successful message deliveries at 9:30 and later were after the walk, with the SPOT unit placed on a rock. This implies that the SPOT unit is more reliable at successfully delivering messages when not attached to a walker.

While graph "SPOTCasting Reception #`1 only shows one test, several other similar tests by several members of the team gave the same results: when in Tracking mode, the SPOT unit did not successfully deliver a number of messages. This applied both in Australia and in several parts of America. We had a number of walks in Tracking mode with the SPOT unit backpack-mounted, fanny pack-mounted, and handheld with reception rates of 17% or lower, including one hour walks without a single message delivered.

Field Test - OK and Help Messages

SPOT Satellite Personal Tracker - Full Review - 15
A field test: the unit was activated a number of times during a simple walk, and the exact times of activation and message reception were noted. The red and blue blocks show where the unit was powered up and was attempting to send either an OK signal (red) or a Help signal (blue). The early OK signals got through (shown by solid red diamonds), as did some of the Help signals (shown by solid blue diamonds). These were often transmitted while the unit was held in the hand.

Between 14:00 and 16:30, two attempts were made to send OK messages while walking along a track beside the sea, on the side of a hill. The failures may have been due to the hillside blocking either the reception of the GPS signals or the transmissions to the satellites, or may have been due to the motion of the SPOT.

The leading hollow blue diamond shows a Help message which was received without any GPS position, indicating that the GPS reception had failed here.

SPOT Satellite Personal Tracker - Full Review - 16
Delay times between button press and message reception during the field test shown in the previous graph (Saturday 15-Dec-07 SPOT Field Test).

The solid red triangles indicate the minutes of delay for each of the successfully delivered "OK" messages.

The solid blue diamonds indicate the delays from activation for the successfully delivered "Help" messages. The messages should have been sent at regular, five minutes intervals, but clearly the SPOT had trouble obtaining GPS readings for most of them. It is also quite possible that some transmitted Help messages were simply not received at all (by the satellites) during these two "Help" attempts.

The hollow pink squares show where two missing OK messages should have been received (shown without delays factored in), but were not.

The hollow blue diamond shows how long the SPOT attempted to obtain a GPS reading before sending the first Help message without the GPS coordinates.

This graph shows the elapsed time between the button press and the message reception. Many of the 'Help' messages, sent at five minute intervals, simply did not get through, with or without a GPS fix. From a safety perspective, this level of message delivery is troubling. We do not know whether this is a SPOT-to-satellite problem, satellite-to-ground problem, or something awry elsewhere in the long chain of communication required to successfully deliver a message.

Tilt Test

SPOT Satellite Personal Tracker - Full Review - 17
Sensitivity to Forwards Tilt (SPOT stationary with clear view of the sky).

Red squares show successfully delivered messages: in general, little sensitivity to Tilt is seen here.

Also shown on this graph are some blue triangles, which show when the 'nearest town' feature was present in the message. It appears that the third-party server which provided this feature occasionally had overly-long delays in response, which caused the message to be posted on the SPOT web site without the "nearest town" information, which is not critical.

Prior to testing, it was not clear how sensitive the SPOT unit is to tilt around the two axes. We know the instructions say it should face upwards, but the unit comes with a belt clip to hang it downwards (antenna facing sideways, which is sub-optimal for GPS reception or successful message transmission). The instructions also indicate how to use it in this position for Tracking mode. Under laboratory conditions, we tested how much this non-face up position would degrade successful message transmission.

The SPOT unit was clamped and operated at various angles. 'Tilt' is defined here as being back and forwards from horizontal: when the SPOT unit hangs from a belt clip, it is tilted.

SPOT Satellite Personal Tracker - Full Review - 18
Sensitivity to Sideways Rotation (or roll).

A solid red square indicates a received message.

A hollow red square indicates where a message should have been received, but was not. The cause of failure is not known in most cases: it could have been a failure in the GPS reception or in the satellite transmission.

A pale pink square indicates where the LED transmit signal was seen on the SPOT unit but no message was received. In these cases we do know that the satellite link failed. The point of this information is that we have seen failures in BOTH halves of the system: GPS reception AND satellite transmission.

Rolling the SPOT unit sideways had a noticeable effect on GPS sensitivity and loss of messages. The data is rather 'noisy,' but that is to be expected when signal reception is marginal. As to why the SPOT unit is sensitive to rolling sideways, we cannot say, but it is most likely an issue involving the antenna used. We do not see moderate tilt sensitivity being as drastic a limitation: in most cases, the user should be able to keep the SPOT within forty-five degrees of being upright. Hanging the SPOT unit on the belt clip is ninety degrees from horizontal, and in our field testing, this had a significant effect on successful message delivery.


"SPOT Satellite Personal Tracker - Full Review," by Alan Dixon and Roger Caffin, with assistance from the other members of the SPOT testing team: Mike Martin and Steve Nelson.. (ISSN 1537-0364)., 2008-05-28 00:00:00-06.


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SPOT Satellite Personal Tracker - Full Review
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Kristen Greenaway

Locale: North Carolina
Sticking my neck out on 06/03/2008 19:35:57 MDT Print View

I've just started to post on BPL after 18 months of sitting in the wings, and I'll probably never be allowed to again, but a question to those who are having real problems getting SPOT signals out. Are you sure you're using the unit correctly? I ask because the first month I used it, I wasn't, and my messages weren't getting through. No Kiwi likes to read the instructions first on any new gizmo, but when I did read them, and re-read again, exactly how long to push each button for and in what sequence, and learn tricks like you can't have tracking on at the same time as sending an OK message, my success rate shot up to near 100%.

Apologies for any slight I may have caused.


Alan Dixon
(alandixon) - MLife

Locale: Mid-Atlantic
Re: Sticking my neck out on 06/04/2008 08:46:07 MDT Print View

The Backpacking Light staff was using the unit correctly.

Long before we started formal testing, we read the instructions numerous times, discussed our experiences with the unit, and corresponded with the SPOT on our initial findings. We then spent pre-review time in the lab and field making sure we fully understood the SPOT's operation and its quirks before doing the field and lab testing that is reported in the review.

I would hazard to say that the BPL review team understood the SPOT's real life operation better than many, possibly most, of the SPOT's staff.


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Sticking my neck out on 06/04/2008 18:17:47 MDT Print View

Hi Kristen

> I've just started to post on BPL after 18 months of sitting in the wings, and I'll probably never be allowed to again,
Ah well, we'll make an exception for you ...
On second thoughts, we won't. An exception would be to bar you, and we only do that to shoe spammers.
You're welcome.

Otherwise, as Alan said.

Terry Wilson
(wilsontw) - F
SPOT Experience on 06/07/2008 15:58:20 MDT Print View

I actually had no trouble activating the unit or using the website. The SPOT has met my expectations. It transmitted every ok message on an April trip in the Grand Canyon including one from my campsite at Bright Angel campground under partial trees near the canyon wall. I had added a number of friends to the email list for ok messages and they really enjoyed following my progress.

I struggled with the PLB vs. SPOT purchase decision and ultimately decided to go with the SPOT - for now at least. I think a future generation of PLB, SPOT or Garmin unit will make all of the current options look poor.

Some of the concerns mentioned - such as email being blocked by SPAM blockers are so easy to overcome. All you have to do is send a test ok message. If you don't get the message, check the SPAM blocker. None of the people in my email notification list have had any messages blocked. The phone messages have also all been delivered.

I did my research prior to buying SPOT and realized it was not a perfect device. For me as a solo hiker, the ok message was the primary expected use for giving my family a little feedback that I was ok. In numerous uses, I have had good results. Of course I can't guarantee it will help me when I need it most. I might not even be conscious to turn it on. Of course a PLB or Satellite phone is also hard to use when unconscious.

Technology progress is never as quick as we want and I have confidence that everyone who buys a PLB, SPOT or satellite phone will collectively keep the progress happening.

Roger Howe
(rogerhhowe) - MLife
Spot reliability poor but fun factor is very high on 06/08/2008 21:17:31 MDT Print View

Congratulations and thank you for the detail review, testing and cautions of relying on a SPOT. I've enjoyed trying to run down the first set of AA lithiums since February. The batteries are supposed to work for up to two weeks! Really, two weeks of being on! Although my personal testing has revealed two of the weaknesses of the Spot, but hey, compared to not having any cell signal and not carrying an expensive PLB and or a satellite phone it is a blast to use! First the weaknesses. Number one, the difficulty in holding a GPS signal while running, hiking, biking and skiing, and number two the frequent tracking messages not making the weblog. To be out on a trek and get one of the ok messages texted to my cell phone in route or returning from the mountain is a kick. Then, logging on at the end of the trip and finding the tracking log has picked up a bunch of my trip points convinces me that although it has many weaknesses, I can see that in a dire emergency there is a great chance that I could get a Help or 911 message out.

The three hints that have helped my experience with the Spot are #1-Place the Spot device on your pack strap with the top pointing down so it approximates the right angle with the sky, #2-You cannot track your position at the same 20 minute time you are trying to send an ok message. Simply hold the ok button down till the green light stays lit, then let it track. When wanting to send the ok, just turn it off, then turn on and give it about 2 minutes, then push ok once. Nearly all the ok messages sent in this manner have made it. If you leave it for the 20 minutes it is almost certainly to be sent, but I usually remain moving as I'm usually anxious to get moving at the beginning, during, and at the end of any adventure when I want to send the ok. Finally #3 hint is forget the lousy Global Star telephone service, it really is not the same as the messaging service. The Global Star reception is extremely poor and spotty, but the one-way messaging is purported to be 99% successful.

I do hope the future will give us better devices that do GPS reception as good as my Garmin 60 csx and also does satellite messaging with more reliablity. Till then I'm satisfied with the functionality and results as they are.

Andy Miller
(andym) - F
I don't want (or need) a tracking device... on 06/09/2008 14:39:13 MDT Print View

I agree with a lot of the suggestions for improvements made in the review - especially about the lack of confirmation that the unit has successfully established its position and that a message has been sent (oh and did you mention the screws on the back?). But I don't want a tracking device - I have a GPS that does that perfectly well - what I want is something I can use to call help when there is no mobile coverage - and from what my own experience with the OK messages the SPOT is well capable of performing that function.

Peter Glaskowsky
(pglaskowsky) - MLife
Great review, thanks on 06/22/2008 16:28:48 MDT Print View

I did my own hands-on review of SPOT on CNET in January ( ) and got similar results-- imperfect operation even with a clear sky, and very poor reliability under any kind of cover.

I also made a set of recommendations, and I hope the SPOT people pay attention to both yours and mine. SPOT could become a very valuable and popular product, but it isn't there yet.

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Mitchell Keil
(mitchellkeil) - F

Locale: Deep in the OC
Re: Satellite phone rental Part 2 on 06/23/2008 10:43:32 MDT Print View

Thank you Thank You Thank You, Jason!!
I called up and arranged for an Iridium Sat Phone for a trip in the Jenny Lakes Wilderness from June 20-22. The phone was delivered by Fedex on the 19th with clear and explicit instruction for operation. The phone arrived fully charged in an aluminum travel case with an extra battery, leather case, car charger, Iridium instruction book and a laminated card with all instructions for operation in any mode. The phone was the latest generation and in spotless condition. Weight as carried on my trip = 10.5oz

I used it with flawless reliability each day in the late PM to call my wife. Spent probably 1 minute each time to let her know how my day had been and that I was safe. The papable sense of relief in her voice was evident. What ever the cost, this alone was worth it!

I just mailed it back this morning at a Fedex drop off store and the return postage was already paid for.

Total cost for all of this including the call time $36.00

I will never look back. I am sold on Sat Phone rental!!!!

Anyone want to buy a SPOT and about 9 months of my service time left......

Chad Schuller
(ckschuller) - F

Locale: In a cube...thinking about trails.
Great Technical Review on 06/23/2008 15:18:07 MDT Print View

love the review!
thanks for taking the time to backup your results with great writing, data points, and graphs.
i'm a newer (M), but i'm looking forward to more reviews like this.

kristin hostetter
(khostetter) - F
Re: bm vs. spot. / iridium on 08/04/2008 08:11:34 MDT Print View

Hey folks,

check out this link for the latest on our SPOT coverage...

Backpacker magazine

R B Rhinesmith
(rhinebr) - MLife

Locale: Rocky Mts
Re: Re: Re: Re: Re: Here Spot! on 08/05/2008 07:45:21 MDT Print View

Excellent review. I just joined and couldn't be more pleased with this type of in depth review and commentary. I agree with the points made in the review and the comments, but would like to offer this new perspective.

I recently used SPOT on a solo trip along the Colorado Trail from Waterton Canyon (Denver, CO) to Copper Mt (appox 105 miles with 17,000 vertical feet). There were sections where I didn't see anyone all day long (but generally there are other day-hikers, through-backpackers, mountain bikers, and some horse-packers along the trail). I used the SPOT to check-in at three predetermined times daily (morning, lunch, and night). I had 100% success rate in sending messages, but I chose the locations to beam an "OK". Usually I initiated the "OK" response right after I woke up or took my pack off. The delay in sending the signal would be 15-20 minutes. I was initially frustrated with the delay, but I think this is tolerable for 1st generation SPOT since there is not a better device at this time to provide "ok" messages to family/friends and hope that future units will be more efficient and reliable. I did not initiate any "Help", "911", or use the "breadcrumb" modes.

Prior to my trip, I set-up to send signals to my wife, daughter, mother, and father. My wife and daughter were in North Carolina working as camp counselors and my parents were "support-team" based in Pine, CO. The "ok" SMS transmissions let everyone know that I was fine and provided my family peace of mind. For my parents, they were able to be more involved in my trip by following me on Google Earth via the email messages. This allowed my father to relieve his segment day-hikes through the same terrain. Also, it helped my father reassess the resupply rendezvous time by sending multiple OK messages the morning we were to meet so he understood the rate of travel and 3 hour earlier arrival time (I took my pack off at Kenosha pass just as he drove up to the parking lot!). Overall my family was excited (versus worried) about my trip and this removes the contentiousness that is typically a part of my adventures. SPOT is a lot cheaper than a divorce lawyer.

I would love to test the "911" in the real-world to check the following:
1. Accuracy of location
2. Ability to successfully transmit in "non-ideal" location
3. Continuity of system to deliver message to response team
4. Total response time from message to help.

Don't give up on this device, but continue to understand its limitations and provide feedback for future products to meet our needs.

Ideal set-up would be SPOT with a PLB...but as I am learning, watch the weight. BTW, I started off with a 65 lb pack and finished with 35 lbs (including food and water for 5 days). My goal is to be sub-30 lbs for the rest of the Colorado Trail. My current weight "hogs" are my backpack (4 kg), sleeping bag (1.9 kg), and sleeping pad (0.9 kg). Ultralight is where it is at for backpacking enjoyment.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Re: Re: Re: Here Spot! on 08/05/2008 15:52:55 MDT Print View

> I would love to test the "911" in the real-world to check the following:

In fact using the Help button will give you exactly the same performance.


Peter Macfarlane
(ptc) - F

Locale: The Scottish Highlands
SPoT? on 08/18/2008 03:45:48 MDT Print View

Good write up of the SPoT. I did testing for it in the UK for the distributor and found it to work well over here, I consistently got 75% or more signals through.
It does need a conformation signal of some sort for casual use and peace of mind.
The 911 function has already saved a life in Scotland so I'm glad that works.
I carry one now so my family can keep tabs on me while I'm out, also usuful for illustrating trip reports with links etc.
The SPoT cause a lot of controversy here when it was launched, but most new kit does. The UK doesn't do "new".

Seattle CG
(SeattleCG) - F
Spot from a Coastie's perspective on 12/25/2008 02:55:44 MST Print View

As a Coast Guard Search and Rescue Controller who is very familiar with SPOT, (also an AT and PCT alum)I wanted to add my thoughts to this forum. I first learned about SPOT with an open mind, but have since found many reasons to dissuade mariners and others to use the device. I can't stress strongly enough the need to go with a 406 MHz beacon, such as an EPIRB / ELT / or PLB as the distress-alerting device of choice. As a reference, I'll point to SPOT's own web site.

Unfortunately, it is full of half-truths and other misleading information.

Below, I've included a transcript of their online video about its "Alert 911" function.

A point-by-point discussion/rebuttal:

Claim: "Every year, emergency authorities conduct 50,000 rescue missions. Many of these people are not found in time. Now there's a way to make sure that they are: the SPOT messenger is the first an only product that combines GPS technology with Satellite-based communication..."

Response: Outright FALSE! Such technology has been available for many years: SARSAT-based 406 MHz EPIRBs / ELTs / PLBs.

Claim: "Whether you are snowmobiling, hiking or sailing, it is your personal connection to loved ones and emergency authorities, with the simple push of a button, from virtually anywhere, worldwide..."

Response: Not always true. You CANNOT depend on it! We here at the Rescue Coordination Center in Seattle had a case in September where a boater's loved ones hadn't received their scheduled "I'm OK" update from the vessel as expected. Suddenly we had an overdue boater on our hands. Turns out the boater had hit the button on the device, but the message was not transmitted. We called SPOT and learned that they were having difficulty receiving transmissions from multiple vessels. Of course neither the sender nor their recipients was notified of this. We had units from Seattle to California involved in this case. Something similar could happen inland.

Claim: "Over 50% of the US does not have cell phone coverage. With SPOT you're covered..."

Response: Um, not always (see above). Also, with any 406 MHz beacon, you're covered, as well. Without the yearly fee and extra fees for bells and whistles.

Claim: "Today, SPOT is saving lives all over the world." (Provides several anecdotes.)

Response: Certainly it has played an important role in certain cases. But show me one where SPOT worked and a 406 MHz EPIRB / ELT / PLB would not have.

Claim: (Case study - the Bertsches) So the wife receives an email stating plainly "This is an emergency. Please send help." Followed by a lat/long.

Response: So this is not to be confused with the message sent when you hit the "HELP" button, which reads: "This is an HELP message. Please find my location in this message below and send for help ASAP." Confusing?

Claim: The wife then says she received a SPOT message saying "I am OK." and was very relieved.

Response: What if she had been away from her computer this whole time? Had she seriously not yet been contacted by authorities? In the case of a 406 MHz alert, the Rescue Coordination Center that receives the alert puts a live person on the phone with the family member / emergency contact as part of prosecuting the case.

Claim: "If your loved one is going into the doors, you need SPOT..."

Response: No you don't. It's a false sense of security.

While SPOT's a neat tekkie tool for tracking someone's location in the wilderness or at sea, it should NOT replace a 406 EPIRB / ELT / PLB for emergencies.

It also lacks the 121.5 MHz homing signal that all 406s have, with homing equipment already installed on all Coast Guard aircraft. Cg boats, civilian air and ground SAR and civil air patrol assets also have this equipment.

SPOT's business model is clearly based on the continued profits generated by its subscription services, and is aligned with the GEOS company, which is in this business for profit (nothing wrong with that).

SARSAT (406 MHz) beacons exist to execute the federal mission of inland and maritime SAR. While beacon manufacturers like ACR and McMurdo look to make a profit, they have to adhere to strict federal (and international) standards to market their devices as SARSAT EPIRBS / ELTs / PLBs. The government (NASA / NOAA) funds and maintains the satellites, and the Air Force and Coast Guard executes all SAR in the US and our territorial waters (and often beyond).

Another aside about the video on SPOT's site: it uses footage of Coast Guard assets that were retired before SPOT was even on the market (44' motor lifeboat / CG HH-65A helicopter [illustrating a case off of AUSTRALIA, and the CG now uses C models with a different paint job]).

Nicolas Costes
(ncostes) - F
GlobalStar: could new Satellite improve the service on 12/25/2008 12:04:43 MST Print View


This article all by itself is worth my subscription several times over.
I am contemplating (or should I say was contemplating) getting a Spot locator for use on my future aconcagua solo climb.
The ability to re-assure left-at-home family is/was a major advantage, tracking would have been fun.

I have used Iridium in various group trekking with considerable confort, but I am not planning on lugging around that equipment solo.

Now, are the problems with getting the SPOT messages through caused by the Globalstart satellites ?

while researching SPOT, I came across a 2007 article:

then, would the new sattelittes solve some of the issues ?
by when ?

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: GlobalStar: could new Satellite improve the service on 12/25/2008 14:04:15 MST Print View

Hi Nicholas

> Now, are the problems with getting the SPOT messages through caused by the Globalstart satellites ?

Not entirely. While new satellites may well improve the coverage and uplink, that is not the only problem with the current generation of SPOT units. There is also the problem of getting a GPS signal in the first place. The article goes into this in some detail.

Imho, the use of one antenna to service both the GPS receiver and the GlobalStar transmissions on the current SPOT means that the sensitivity of the GPS receiver has been seriously reduced. It cannot get a GPS signal in many places where other units can. We tested for this and clearly demonstrated it. Without a GPS signal the current SPOT will not try to transmit an OK signal. Its Help and 911 messages are equally of very limited use without a GPS signal.

Does this mean that a next gen SPOT unit might be able to overcome all these limitations? Possibly so, but just upgrading the satellites will have no effect on the GPS bit. That said, we do look forward to the possibility of an improved unit at a far lighter weight.


Nicolas Costes
(ncostes) - F
is it the GPS ? or the satellites ? on 12/25/2008 18:50:10 MST Print View

Thanks for your speedy comment.

The article is very well documented. It lists the various downstream components, which all have to work for the localisation/alert service to occur.
In particular, you have underlined that OK signal can not be send if no GPS fix is available, and that there is a limited amount of retry.
The failure to send a message can very well be caused by a single cause or a combination of causes.
You have identified several potential, among which the antenna being optimized for satellite communication rather than GPS.

I have tempted to investigate the following:
1. Antenna.
The uplink occurs on the L-Band at 1610 MHz.
(the L-band elements seems unaffected by the satellite troubles according to
The GPS signals come down also in the L- Band at 1575.42 Mhz
I am tempted to believe that an antenna small enough to fit in the package of the globalstar Spot and good enough for 1610 would be ok for 1575. I could be very wrong because the problems you described with not getting a fix could be cause by poor discrimination of signals rebounding (multipath elimination) where a very well tuned antenna helps)
Yet the GPS component is known and acceptable performer when used in handheld GPS.
But of course an antenna is not just a wave guide. There are additional electronic elements that would first split and then amplify the signal. There may be an issue there in how the same antenna is used for reception and for emission.
see pic of Antena and other tests at

B/ GPS receiver
Regarding GPS location, the computation is done by a Nemerix NX2 /NJ-1030 chipset
(don't know the revision, back in 2005, the previous gen software Version V2 had lot of problem with multipath reflection, version 3 was supposed to be slightly better). Nemerix is not as sensitive, nor as compute-heavy as the its competitors (such a SirfIII), but is very low power.

C/ GPS first fix
I don't know wether the Nemerix keeps the almanacs of GPS in memory between attempts to message, (meaning that the GPS could be attempting a fix from cold everytime). but failure to get a fix witin a reasonable short time could hint at the GPS being unable to get a strong signal from one satellite from which to get the almanachs.

I am troubled by the existence of the ON button.
Why should you have a ON button if the power hungry options of getting a GPS fix and sending a message are controlled by other buttons ?
I wonder if the unit does not get the GPS almanachs while switched ON, or rather if it does not keep in memory while it is left ON the latest almanach it downloaded during the last succesful GPS fix. Unless mistaken an almanach is onnly valid for 6 hours.

You have done a very exhaustive set of tests.
Would you say that the performance od sending a OK signal was better if:
- unit was switched on at time t
- key is pressed t+5 (letting teh unit tried to get a fix by itself ?) (does the LED display changes to show that a GPS fix has been aquired ?)
- unit is switched off (or moved ) after led signals signal is send (or 2 more minutes).
or was it better if you basically left the SPot always on ?

because the "send help" message does not alert 911, but can go without a gps fix, I think that to test the downstream elements (uplink to sat, sat, to base, base to SMS), you could try to send only "send help" message in openair environment.
If you still have 80% success this means the trouble is with the downstream. If you have 90%+ this mean that the "OK" message are hindered by the need to get a fix from the GPS. If you have varying success at different time of the day, this may mean that the unit - satellite link is not strong enough (no satellite visible / poor power/poor directivity from unit / poor discrimination from satellite / base station available).
The GPS fix/ no message received which happened when the received was tilted points indeed to poor uplink link.

Were you able to SMS back your own message to your mobile phone (to get a feedback wether or not the message was received or not) ?

Edit: I found a very informative post of information coming from a Spot engineer (the original posts were removed, but someone was fast enough to capture them)
the post is there: (I do not know wether it is appropriate to copy content or URL), the info is quite important.
A good mathematician could come up with it based on the published information of the constellation of GlobalStar satellites.

copy from
From a thread with over 450 posts at advrider I condensed the following "rules" for use of SPoT.


The device is totally dependent on being oriented correctly to function as intended. There isn't an external antenna as with a PLB to give an indication of orientation. Keep it flat and free when a button for action has been pressed.

Global star satellites can be tracked real time on

If you are at a high latitude up north (above about 63 degrees), it serves to have a mental image of what is needed for successful transmissions: You need a wide open view towards the south within say +/- 70 degrees down to about ten degrees above the horizon. Within this sector, a lone satellite will appear for a couple of minutes to pick up the transmission. It will pass going east in a slightly curved trajectory, the lower above the horizon the further north you are. Then there will be some minutes until the next satellite appears which can be anywhere in the sector. Below 52 degrees latitude, satellites can be found all the way up to directly overhead but it is more important to have a free view to the south than the north until you come in well under coverage (approx. 40 degrees latitude).

Trees have a very detrimental effect on transmissions , more so than on GPS reception. Moreover, the Global star satellite you need often appears lower on the horizon than GPS satellites which makes the passage through canopy longer. This effect is exacerbated as you move to higher latitudes.

Each transmission only lasts a second and when the LED lights up to indicate transmission, it has already occured. If there was an obstacle between the SPoT and the satellite at that moment, the next opportunity is several minutes away.

Don't look for confirmation that messages have been sent, since transmissions occur repeatedly over a period of time to increase the chance of reaching a satellite during its passage. Messages have been sent when the corresponding LED stops blinking. The GPS receiver will shut off when the transmisssion cycle is completed only to be turned on the next time you demand an action (cycle time: OK 20 minutes, HELP 60 minutes or 911 forevever, i.e. as long as the batteries last or you cancel or turn it off).

After having pushed a button for transmission, check the unit after some time (10-15 minutes) to confirm that there is a GPS fix (LEDs still blinking synchronously).



Conclusions: A great device when used below say 60 degrees latitude and there aren't trees around that can interfer with transmissions to satellites with low elevations.

Nicolas Costes
(ncostes) - F
found info from self-proclaimed Spot engineer on 12/25/2008 19:53:41 MST Print View

Google is our friend:

read the posts from Spotmaker

Hi Adventure Riders!

I work for Axonn LLC, the company that designed and manufactures the SPoT. I am one of the engineers that designed it. I'm loving seeing the response that it is getting! Lots of folks seem to be excited about it.

Here are a few tips for it's use:

The "check in" message actually transmits THREE TIMES. It transmits in the following pattern: As soon as the SPoT has a GPS fix it transmits, then 5 to 10 minutes later (randomly dithered) it transmits a second time, then 5 to 10 minutes after that (random again), it transmits a third time. These three transmissions all have the same internal packet ID which causes the SPoT back office to throw out the duplicates and only send one to the emails and cel-phones on your check-in list.

As a result, this coverage map:

Shows the probability of a check-in message getting through!

How do you know when it's done sending all three messages? Simple, the "ok/check" LED stops blinking! So, it's best to send check-in messages from your base camp, or when you've stopped for a few minutes to admire a view. Activate check-in mode and leave the SPoT sitting with it's face to the sky until the ok/check LED stops blinking.

The coverage map also shows the probability of at least one out of any three consecutive help or 911 messages getting through (at 5 minute intervals, help and 911 will have transmitted 3 or 4 times in 20 minutes, depending on when you start measuring the time). Each help, 911, or track message is only sent once, but a new one, with fresh GPS data and a new packet ID (causing the SPoT back office to pump all of them through), is sent every 5 minutes for help/911 or every 10 minutes for track.

Offroute is exactly right in his assumptions as to what it means that the satellites are moving around in the sky. For a message to go through, at least one satellite has to see your SPoT, and see one of the SPoT ground stations! What this means is: if you've got a great horizon-to-horizon view of the sky, and you're not too close to the edge of the dark orange area in the coverage map, almost 100% of your "track", "help" or "911" messages will get through. If you have only a partial view of the sky, or you're starting to get near the edge of the dark orange area of the map, the condition of a satellite being in view of both your SPoT and the ground station happens somewhat less often, so fewer of your messages will get through.

But: since the satellites are moving around, time is your friend. If at one moment in time, there is no satellite in a "good" position for you, the odds are very good that 5 - 10 minutes later one will be! So, since the check-in message is actually transmitted three times, we've measured that throughout most of the US and Canada the probability that the check-in message will get through is around 99.99% (you'll miss something like 1 in 10,000). The likelihood that at least 1 out of any given 3 consecutive help, 911, or track messages will get through is about the same.

n order to make the unit as 1)small, 2)light, 3)inexpensive and 4)power efficient as it is, some design choices were made that traded off raw acquisition time for smallness, price, and improved battery life.

There's also an internal delay of a total of 30 seconds after an actual GPS fix is obtained before we transmit for power management reasons. (So, when you see it transmit, it actually had a GPS fix 30 seconds prior.)

The satellite transmitter within the unit is a major power sucker when the messages are being transmitted to the satellite. This resulted in the other parts of the unit having to be extraordinarily power efficient to compensate.

The GPS subsystem in the SPoT uses an infinitesimal fraction of the power that the equivalent subsystem in a hand held GPS navigator uses, for example.

So, raw dead cold start on a SPoT is a little longer than the best of the newest GPS navigators.

What's a "dead cold start"?

That's when:

* The unit hasn't obtained new almanac data from the GPS satellites for more than 30 days or,
* The unit has been moved more than about 600 miles since the last time it obtained a fix.


well a last tidbit which answers my one question
As a result, that antenna is optimized for it's radiation pattern on the transmissions to Globalstar's network (otherwise, they wouldn't have certified it) and sacrifices a little bit of pattern symmetry on the GPS (compared to a dedicated GPS antenna). Interestingly, GPS gain is biased slightly in the direction of the buttons and LED's, ..

The transmit pattern, on the other hand, is an even broad cone-shaped pattern. It's very close to Globalstar's ideal example of what a simplex transmit antenna is supposed to do on their network.

Maybe, but be careful not to overdo it. The radiation pattern is very broad. With the unit flat on it's back, the pattern is quite even in a cone from about 10-15 degrees from horizontal to 90 degrees straight up. So, if you tilt it more than 10 - 15 degrees, you're doing little more than sending potentially useful RF energy into the ground.

Safest bet for optimum transmission performance is always to have the unit laying flat on its back. However, if you're at a latitude greater than 45 degrees north or so, a clear view of the southern sky is important. The further north you go, the more important a clear view to the south is and less important the view to the north is.

The unit puts the GPS chipset into a "standby" mode between transmissions to save battery power. In this standby mode the Real Time Clock still runs and the ephemeris and almanac data are retained. As a result, after a shut off of only 10 minutes, the restart is what is known in the GPS world as a "hot start", and assuming the GPS signal strengths are at all trackable, it re-acquires them in about 1 - 5 seconds.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: is it the GPS ? or the satellites ? on 12/25/2008 21:02:50 MST Print View

Hi Nicolas

> an antenna small enough to fit in the package of the globalstar Spot and good enough
> for 1610 would be ok for 1575.
One would certainly think so, in that small a volume.

> There are additional electronic elements that would first split
Yes, sharing one antenna between two devices means that there has to be a coupler of some sort, and the coupler will have significant losses in the antenna to GPS Rx path.

> Nemerix is not as sensitive, nor as compute-heavy as the its competitors (such a SirfIII), but is very low power.
Yes, we had noticed the lower sensitivity. Not a good design decision imho.

> Would you say that the performance od sending a OK signal was better if:
> - unit was switched on at time t
> - key is pressed t+5 (letting teh unit tried to get a fix by itself ?) (does the LED display
> changes to show that a GPS fix has been aquired ?)
> - unit is switched off (or moved ) after led signals signal is send (or 2 more minutes).
> or was it better if you basically left the SPot always on ?
If I remember correctly, you have to wait about 5-10 seconds after you press the ON button before you can press the OK button anyhow.
There is NO direct feedback about the GPS fix. If you watch the Tx LED carefully ALL the time you may see the transmit signal briefly. This only happens IF the GPS fix has been acquired.
If you switch the SPOT off after the first Tx, you have lost all the GPS values and have to start afresh the next time.

> you could try to send only "send help" message in openair environment.
We did a lot of this. There are graphs showing our test results in the article. Not all Help messages got through.


Tom Tessier
(ttessier) - F
Iridium 2-way tracker vs. Globalstar one-way on 12/30/2008 15:14:54 MST Print View


Your review corresponds to testing I did a few years ago with the technology. You really went through a lot of work, that's great.

After experiences working in the Canadian arctic and seeing that nothing really worked for long term use, I decided to build my own tracker with 2-way messaging.

Four years ago my partner at the time and I tested the Globalstar SENS technology using a unit that uses the same Axxon chip that SPOT uses. At 62 degrees north, we could never get more than half the messages through. We also didn't feel good about not knowing our messages were making it through.

At 50 degrees north, it was a bit better but it still didn't have the "positive connect" that we decided was what we would need to feel that it is "man-rated" for safety (my background is in space engineering-we worked on a few Shuttle experiments where "man rated" was an actual standard).

The simplex technology is cool, low in power use and very light in weight (as compared to other satellite technology - except maybe ARGOS bird trackers which are an ounce or two but not for public use). But then, you would expect low weight and power use as it doesn't do much else but transmit a short burst. No receiver or message buffers to take power, and the transmit does not require a handshake to a satellite like other systems - it's really simple. But, that's partly why I wouldn't use it for people safety. It's a fantastic technology for non-critical tracking - cheap, easy to implement. But boy, was I surprised when SPOT came out - I still say they are really taking a big risk with this.

So, for tracking people for safety reasons at least, we dropped the Globalstar technology and looked at Orbcomm, the only other relatively light-weight 2-way messaging technology available at the time. Works good, but the latency was s-l-o-w. At least 15 minutes at mid-latitudes.

Finally, Iridium came up with Short Burst Data. Two years ago, I started work on this, and the more I worked with it, the better I liked it.

After a year of beta testing our design, and making a lot of changes, we have the Field Tracker 2000. I think some of you would be interested in the details, but I won't put them here - they're at .

The unit is a portable two-way communicator with text messaging and an interactive display, including GPS readout. Our first unit is a pound and a half, and we're coming out with a lighter design that will be just under a pound. With the limitation on the satellite radio we have to build into this unit, we really can't make it much lighter and still have a screen.

The unit is professional quality, so is not cheap but it's built for rugged use. We could go to lithiums in a variation of the design to save a bit of weight. We didn't do that with our first unit because this would make it a Class 9 dangerous good on aircraft - some pilots, especially in the north, don't allow lithium batteries on board.

Looking at the review on SPOT, I see a lot of great comments. We have had some pretty comprehensive testing by third parties of our beta units and have implemented a lot of improvements as a result. Maybe BPL would be interested in testing one of our lighter units when they come out.