I carry an Acme Tornado because it's small, light, and "loud enough." It seems louder and easier to blow than a Fox Micro 40, which is a similar size.
A New Zealand SAR group tested how far (in meters) whistles could be heard in the dense NZ bush:
Acme Thunderer 400
Black Pea 338
Turbo 2 SAR 263
Note the limitations of the yell or scream in someone else's tests:
Human Scream (pees after coffee or soda)
Adult Average: 107 db
Child Average: 104.3 db
*NOTE* Our adult tester, Kevin Estela (aka Estela216, a Moderator at KnifeForums), screamed three times the first at 110db, the second at 107db, the third at 104db. After the third scream, his voice was notably affected. By the next morning, he suffered a slight case of laryngitis from the event. Important to note! CARRY A WHISTLE!
Our young adult tester, Becky Two Knives, screamed three times, the first at 101db, the second at 107db, the third at 105db. During her second scream, she belted out a change in tone that didn't even register on the decibel meter. That scream damaged the hearing of all present and scared the coyotes off Marty's property for a night.
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