One of the "10 Hiking Essentials" is a whistle. You're in a precarious situation, you are lost, and you need to signal to others - the whistle is an important element of being on the trail. Think about how you will signal for help if you have a traumatic fall, don't could on yelling for too long. Plus the whistle will project quite a bit further.
We believe that every Hiker and outdoor enthusiast needs two whistles. Every whistle has a different tone, pitch, and volume. They all vary and frankly, some just don't measure up; they can be muddled and dull. When the situation calls for it, you need something with a little extra oomph and sometimes you just need an even keel attention grabber that's not startling.
The Acme 210.5 (not 210, not 212, the 210.5) has a great pitch. It's not too loud and not too soft. It's less intrusive and does the job for anything that is required in close vicinity without too much disruption. Whereas the Fox 40 Sonik Blast is just that, it's loud, it's jolting, and it gets attention. If you want to replicate being an NFL official standing on the 50-yard line of Superbowl 30 - this is your whistle.
Whatever you do, just make sure that you have a whistle in your hiking pack for safety reasons. If it's more than that, this is a good balance.
P.S. Our favorite holder for these is the Gear Keeper Hammerhead.
Get outside and happy hiking!