Automatic NXT Light Switch
From the creator's description:
"It works by attaching two long pieces to a motor. It must be stable so I lifted it up and taped it down. Finally I attached a cord from the motor to the Mindstorms main unit...I programmed it to listen for sound to turn it on and off."
(EDITOR'S NOTE: I don't see any sound sensor, but I'm sure that one could be added).
More pictures are