This app is designed for people with Nerf/airsoft/gel ball guns who want to play some bomb defusal IRL.

To play, split your group into two teams, Terrorists and Counter-Terrorists. Just like in the original game, one person on the terrorist team starts with the bomb.
Tap anywhere on the screen and a loud beeping noise will indicate the start of the round.
The terrorist team plants the bomb at a predetermined area (discuss with everyone prior to game!) by holding down on the screen until it is planted.

After the bomb is planted, the counter-terrorist team tries to defuse the bomb by holding down anywhere on the screen. A progress bar will appear, and when it reaches 100% the bomb is defused.
If the bomb is not defused in time, an explosion effect plays and the terrorist team wins.

Alternatively, in the options menu you can switch to keypad mode, taken from the game Pavlov VR. In this mode, instead of holding down on the screen, people planting or defusing will need to press the corresponding digit shown at the top left of the screen.

Be sure to go through the options menu, there's quite a bit of customisation. You can set how long each phase lasts, amount of time required to plant and defuse (or amount of numbers to press), the loudness of each sound effect, and you can disable the hints and change the FPS the app runs at.