@EnriqueGlza Put on a hood. Lock the hood shut. Push the buttons on the lock behind your head. Wait for the time to count down (and hope you didn't push those buttons too many times). And no cheating by using a mirror.
@OliverSelfSlave I assumed that the timer lock was going to count down to zero... and then you were going to roll over on your back and accidentally trigger it to lock for even longer.