While we are on this subject, my public service announcement. Those of you who go hiking, even if it's a micro-hike....
Check your pack. Look at the buckle on the sternum strap (it goes across your chest). It may have a built-in whistle. If it doesn't, you'll need to tie a whistle to your pack, preferably within easy reach of your mouth (also, if boating, your PFD).
The whistle sound carries much further than a voice.
I can't find my photo, and I don't currently have a pack with a whistle on the buckle, but here's a visual.
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