Did you ever wonder if your device is really waterproof but do not want to find that out by dunking it in water?
Here is a test which uses just the phone and it's service mode (or any barometer app).
1. dial *#*#7378423#*#*
2. go to "Service Tests"
3. go to "pressure sensor"
4. slightly compress the phone using your thumb and index finger by pressing on the display and back
SLIGHT PRESSURE. No Berserker mode please! This is not a crush-your-phone contest!
--> if all seals are intact the pressure should rise. Your phone with intact seals is a closed system. If you compress the volume the pressure goes up as a result. If any of the seals is compromised pressure will not rise.
Note: pressure will decrease automatically - that might be a result of the sensor adjusting, it will not go back to it's original value until you relieve the pressure.
credit for the original idea goes to User Alik from the German Android-Hilfe.de forums