I have one of the sternum strap whistles, and they're strictly the backup of a backup. I keep the 636 as my rangemaster whistle because the biting tone cuts well through background noise.

For pealess whistles, I like the ACR for giving the loudest blast for the lightest blow, and the "lifeboat" whistles for carrying distance. But, my go to rescue whistle is the big storm whistle. Attracting rescue should not involve subtlety.

Someone who had given it more thought then I have.

https://bigpigblog.com/2014/06/13/whistlemania-iv-sound-off/
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Hope for the best and prepare for the worst.

The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane