The Kingii is an emergency life preserver that you can strap right to your wrist that inflates in seconds and brings you straight to the surface of the water.
http://odditymall.com/kingii-wristband-emergency-flotation-device
This is such a good idea and maybe the manufacturers should design a way to make it automatically inflate if someone passes out but idk how you would do that
To do that, they would need to have a heart rate moniter and if it drops below a specific BPM, it would automatically inflate