Strobe

Flashing electronic device, similar to the strobe "flash" on your camera, this waterproof unit flashes roughly 60x/minute at a high intensity.

While not recognized as an "official" offshore emergency signaling device, activating one is sure to be noticed. It is an officially recognized inland distress signal and using a strobe on inland waters for anything other than distress is illegal.

There are also stobe units that will flash out SOS in Morse Code.

Do not use a strobe that flashes at rates other than about 60/min. These can be confused with navigation aids and are not permitted.