Nauticalia

If you might want to find or identify it when it's dark - keys, lifejacket, kitbag zipper, end of the boom, a torch, your pet who's always in the way, or a light switch - attach one of these. They are self-illuminating safety devices, powered by a Tritium gas system which never needs recharging from another light source and lasts at least 10 years.

They can be seen from 30ft and thanks to their tough polycarbonate shell, are submersible to 90ft. Length 2".