Dive Alert Plus
Small and lightweight signaling device that attaches to your BCD power inflator hose. Emits loud signal both in air (on the surface) and in water (underwater). Above water, the horn will be heard from 1 mile away. Underwater it can be heard about 100 feet away, but this will be less if your dive buddies are wearing hoods or anything covering their ears.
The DiveAlertPLUS quickly attaches to your dive gear with no modifications required and does not interfere with normal operation of your dive gear. To activate the loud horn, just simply squeeze the device.