Oh, Oh, Oh those are cool. I am a certified diver and we have a very similar item called "spare air". They are about the size of a 12oz soda or beer can and have about 10 breaths at 30 feet. I use mine for snorkeling, very cool. I had to get one once I saw them. They are really meant to be used as a backup to your main gear, enough to get you to the surface from about 150 feet. But very cool if you don't want all the gear for a quick dive. Also great for inspecting the underside of large boats.
Brock
[This message has been edited by Brock (edited 08-19-2000).]