Navimate GPS for Divers
Navimate is a product in development that claims to be able to estimate a diver's GPS location using radio signals from buoy. It's not for sale yet but on their website they claimed to be for sale starting in 2016. Not sure what the holdup is. Here is a diagram of how it works. Navimate has a cool looking wrist mounted computer. This computer is supposed to be able to relay your location and air supply to your dive buddies and the boat.