Here's what other sites are saying:
Strap the ACR WW-3 Survival Whistle to your pack or PFD, and you'll be heard in an emergency. The WW-3's flat, bright orange design is lightweight and visible in low light, so there's no reason you shouldn't have it close at hand. Dual chambers flush water and debris easily, and the shrill dual tone can be heard over rushing rapids, high wind, and engine noise. Currently in use with NASA and the U. S. Navy, the ACR WW-3 Survival Whistle is USCG and SOLAS approved.
Gets attention!Loud, shrill, dual tone audible from great distance.Unique flat design prevents holding water.Required by SOLAS 83.Meets USCG/SOLAS requirements.Aids in land or sea rescues.Use on life jackets, vests, foul weather gear, ring buoys, rafts, keychains, etc.Developed for the U.S. Navy; used by NASA, major airlines and shipping companies.Complete with 18 in. (45.5 cm) of lanyard.
ACR Signal Whistle
NRS Storm Whistle
Vargo Titanium Emergency Whistle
Harmony Fox 40 Whistle
Coghlan's Four Function Whistle
$3 - $4
Coghlan's Plastic Signal Whistle
Coghlan's Safety Whistle
Coghlan's Wilderness Signal Whistle