With all the already used electronic for navigation, we can also integrate safety methods:

Some issues seems to be:

- UV light: Reefs are sensible to UV protection sprays and lotions, a warning if to long exposed to UV light should be necessary, which can be done with an UV sensor and timer.

- Tides: Depending on time, a warning can be issued when tides change (as well as using the timer to regualting snorkeling duration).

- (The wireless connection could allow to call for help in emergency situation, but since you can't count on it that's not a real safety feature)

- The most interesting part might be the shallow water blackout problem, since the problem is that there exist no indications besides no movement, which are hard to detect when movements can be also happen passive because of tides or waves. At the moment we tend to integrate a capacitive sensor area on the snorkel, detecting the water level inside: If it stays a certain time without getting air inside in between, we would then first activate a haptic warning for sort of a dead man switch (user has to press a button to prove he is still conscious), otherwise a warnign will be sent (optimal would be then activating a self-infalting live jacket to get the head  directly above water)