A timer is a mechanism that can be used to have events occur after a period of time.
ExampleEditIn this example, the first switch (which is On) will power the electric field, and the door thus keeping it closed and blocking the cat. As soon as the burglar steps on the switch, the electric field is powered off, and the cat is released.
The burglar will now think it's safe to continue, but in fact the cat will head to the right, and reach another switch (which is initially Off) before the player can reach the vault. The electric field will power on and kill the burglar.