I like having a whistle for out in the field.
If your dog is a good distance away from you, or it's a windy day. A whistle is going to carry a lot further than your voice.
Over the years, I've used quite a few different ones. As long as it's a sharp, crisp, clear whistle sound, it doesn't matter. You want to make sure you buy three or four at one time. Put one in each vehicle, and one where are you normally keep your leashes. I also try to keep one in my hunting bag.
Most of us use acme, but you don't have too.
Not all those who wander are lost.
Life is just a leap of faith.
Spread your arms and hold your breath and always trust your cape.
Two things define you. Your patience when you have nothing, and your attitude when you have everything.