Looking for possibly the smallest and lightest whistle on the market? Well, check out the Titanium Whistle by 4Sevens. It is an investment at $20, but the return is a 100 decibel pea-less whistle about the size of a few wooden matches. It weighs .2 oz, or 5.6 grams. As far as I know, this is the most elite of whistles for lightweight backpackers – small, loud and light, and let’s not forget it will meet the demands of those with a titanium fetish.
In the picture, the Fox whistle is what I've carried after evaluation of approximately 8 other options. One thing I'll miss with the switch is where to put my button compass.
With a whistle this size, there is no reason anyone shouldn't carry it just for the sake of safety.