I have a couple. They are extremely loud but also quite big for a whistle. I attach them to my Jeep key rings because they also make the keys almost impossible to lose.

I have been reading this site's Gear & Equipment section and refreshing my knowledge on knives and some other gear. If you haven't looked at it, it has great info.

The whistle section, which mentions the Storm and its smaller cousins is here: http://www.equipped.org/signal.htm#SoundOff