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iPhone GPS: disabling cell service
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Casey Saenger
(csaenger) - F
Re: iphone as GPS on 04/26/2014 16:53:18 MDT Print View

My wife and I have been considering replacing our Garmin with an iPhone for an upcoming Brooks Range trip and this has been a very useful discussion. Amy's suggestion that the SIM card be disabled or removed to preserve battery made me wonder if the SIM card was necessary for GPS? I'm currently a dumb phone user and wondered if I could get by with an unlocked iPhone 4 if I acquired Gaia via Wifi before heading out.
Sorry to be so naive.
Casey

Mitchell Ebbott
(mebbott) - F - M

Locale: SoCal
Re: Re: iphone as GPS on 04/26/2014 17:50:13 MDT Print View

Casey, the SIM card is only for cellular service and is not necessary in order for the GPS to work.

Amy Lauterbach
(drongobird) - MLife

Locale: San Francisco Bay Area
Re: iphone as GPS on 04/26/2014 17:57:13 MDT Print View

As per Casey's question -- Amy's suggestion that the SIM card be disabled or removed to preserve battery made me wonder if the SIM card was necessary for GPS?

To clarify a common misconception: You do NOT need WIFI or Cellular connection for the GPS chip to work; however you do need to have pre-downloaded the map content in order to have your current location show up on a map. You do NOT need a SIM card for GPS; they are separate chips.

The instructions in the article are still true. http://www.adventurealan.com/iphone4gps.htm

Casey Saenger
(csaenger) - F
Re: Re: iphone as GPS on 04/26/2014 20:04:17 MDT Print View

Thanks for the info, and sorry to make folks reiterate what's been typed elsewhere. It is just so contrary to what Dustin told me at the AT&T store this morning that I wanted to be explicit.
Casey

Amy Lauterbach
(drongobird) - MLife

Locale: San Francisco Bay Area
Re: Re: iphone as GPS on 04/26/2014 20:53:26 MDT Print View

It is just so contrary to what Dustin told me at the AT&T store this morning that I wanted to be explicit.
Too funny. When I bought my iPhone the sales rep at the Apple store assured me that GPS would not work when there was no cell signal. I had read so much that was contrary to that; in the end we agreed that the 30 day return policy meant that I would trust what I read and not what he told me :) I think a big part of the confusion is that if you don't have maps pre-downloaded, then when you open a map app it will look like it doesn't know where you are. Apps like Gaia GPS solve that problem by letting you download all the maps in advance.

And last year when I was working with the folks at the genius bar to figure out the battery drain problem with locking the SIM on an ATT iPhone 5, the "master genius" assured me that I could turn Airplane mode on and GPS would work as long as I had WIFI on. I tested that, and as I expected, it doesn't work -- it is true that you get an approximate location as long as you have a WIFI signal, but once you're out of WIFI range then there's no location info.

The iPhone has "Assisted GPS" aka A-GPS . You can read what that means on the wiki article. The iPhone ALSO has standalone-GPS (which is disabled in Airplane Mode) as well as WIFI Positioning system (which gives approx location if you have WiFI signal but are in airplane mode and thus GPS is disabled). WIthout a SIM card (or with card but no cell signal) it will take much longer to get the very first fix after you power up in a new location -- in my experience it's as much as 3 or 4 minutes. But after that very first time, it subsequently takes 20 or 30 seconds to get a GPS read. It's good to know about the slow first fix -- don't panic, just be patient.

Believe me, we folks who care about 1) battery life; 2) GPS reception; and 3) NOT cell signal -- we are so small a group that we are not on the ATT or Apple radar.

Edited by drongobird on 04/26/2014 20:56:26 MDT.