Yesterday I found a website about diving computer. Because I'm not a diver I have no glue about them but it looks like even there is a market for wearable computing.

Beside many functions I found this here:
You're at 80 feet with 1300 psi remaining in your cylinder - how long before you need to begin an ascent to a shallower depth? Our patented Air Time Remaining feature calculates your current depth, breathing rate, cylinder pressure, ascent time, and decompression status to tell you exactly how much time you can remain underwater.

It's not like a lifetime guarantee but at least the best technology available today.

The same works for the remaining dive time (Dive Time Remaining, like Air Time Remaining provides a 'real' number in minutes, considering Air Time Remaining, Nitrogen and Oxygen absorption, and automatically displays whichever allows less time.)

More features here: Oceanic Worldwide - Scuba and Snorkeling Gear, Scuba and Snorkeling Equipment and Dive Gear