In case you have something to say, and say it loudly!
Your ability to signal for help is the number one factor in being rescued. Carrying a rescue whistle on your person is an inexpensive and easy way to identify yourself as being in need of rescue and being found.
One of the safest forms of personal protection is a loud whistle. A whistle can’t be turned against you like many other personal defense tools. People have been conditioned to know that the sound from a whistle is a call for action and it instantly gets their attention. Carry your keys on this key ring to be safe.