The best underwater signaling device is the Scuba Diver Alerting Device. This type of alarm creates a whistling sound when submerged, and it can be used for up to two hours before needing replacement batteries.
The Best Underwater Signaling Device is a Scuba Diving Noise Maker
They say that the best underwater signaling device must be able to work when submerged. For this reason, divers use noisemakers which they attach to their scuba gear. They make all sorts of noises depending on what kind of alerting signal would be most appropriate in any given situation; these signals are not only heard by other divers but also marine life like whales and dolphins who may need help or instruction from humans as well!