I tried pumping air into my PlaySport depth tester, but didn't see any change in the pressure gauge as I did so. That concerns me, as I wonder if I would be able to detect the pressure buildup before it reached explosive levels. As someone noted in an earlier post, the ABS pipe becomes a grenade at high enough pressure levels.
Below is a possible solution to the worry. 30 PSI is 2 ATM, equivalent to 60' underwater. If I used a pressure relief valve on my PlaySport depth tester, I wouldn't need an air pressure gauge.