Install the app on a phone that one of your friends will use, set the timer and start the prank. After a while, a screen crack sound will be heard and the phone screen will appear broken. Even if your friends figure out that this is only a prank, the app won't appear on the running apps, so they will not be able to stop it.
In order to stop the prank, open it again.
App name will appear as "BScreen" to make it harder for other people to stop it.
More realistic than other cracked screen pranks, app will not appear at the running apps so it will be hard to stop the prank. Easy to start and stop the prank - stopping is done by opening the app again.