This is an animatronic coffin for a client as a Halloween decoration. Here you can see the basic case and the internal pneumatic piston that opens and closes the door.

This is the brains of the unit, hidden in a recessed area in the back of the coffin. It is controlled by an Arduino R3 microcontroller and triggered by a passive infrared motion sensor. When the infrared sensor picks up motion, it sends a signal to the Arduino which trips a solenoid that allows air to flow into one end of the piston, opening the door. After a few moments the solenoid trips back to it’s original position and air is pushed into the piston from the opposing end, closing the door.