Thinking about your situ some more, a quick search turned up a page
plus worth of "waterproof" key holders/wallets, etc. :
http://www.waterproofcases.net/603.html

In my 400+ dives, I'm not sure I'd trust them though...it is one
more thing to attach to yourself or, lose out of a BC pocket or...
And, any dive below 33 feet starts to put some serious pressure
on that container. I still think I'd pass on taking a smart key
under water, fresh or sea water...