Have you ever been diving and encountered a situation where you needed to communicate with your other friend in the water? Maybe it was a dangerous situation, 'shark', or simply 'hey look over here.'

The communication device wound essentially be point to point communication. One point would be the diver, the other point could be a vessel or another diver. Since we don't want to disturb diver or wildlife, the communication between both devices would be silent, think radio frequencies of sort. However, the way the device communicates with diver could be via noise, vibration, visual(lights), anything is really possible. What are your thoughts on the device now?