To set up Fingerprint Screen Lock, you have to choose a background image from the six different ones available, and choose the number of flashes it will show (the fewer the better). When you touch the screen with your finger, the screen starts flashing; if you let go after the exact number of flashes you chose, the screen unlocks. It's that simple.
The app is not an actual lock screen, so if you just press the home button you can skip the previous processes.
Fingerprint Screen Lock is a fake lock screen that lets you prank your friends, although it's not very useful as a real lock screen.
Requires Android 2.3 or higher