The app works by simply sensing pressure, via the inbuilt barometer with users asked to press the screen with both of their thumbs. If the phone is fully sealed, the pressure inside the device will increase, it’s as simple as that.
Now, you might be wondering if it really works, but judging from the Play Store reviews it seems plenty of people are seriously impressed.
“I have no idea how it works but it does lol, at least in the 4 test cases i tried. Xperia 5 II (IP68, intact) – waterproof(not waterproof if sim tray is removed); Xperia XZ (IP68, corner busted open, screen replaced) – not waterproof; Galaxy S4 Mini (no IP rating) – not waterproof; Awesome app.”
Whilst another added: “Genuinely a very brilliant and simple app, have to hand it to the developer for using the barometer in such a smart way. Tested a Galaxy S10+ (intact) Tested a Pixel 2 xl that was dropped and damaged and said it was not intact. It’s not just looking up the device model, it’s a real test.”