In the Make magazine blog, Phillip Torrone talks about Claude Shannon’s “most beautiful machine” that has one function only. When you turn it on, it turns itself off.
When I was a kid, there was a mass-produced toy that did this. Flip the on switch, and a hand came out of the toy and flipped the switch off. I think it was based on “Thing” from the Addams Family. I couldn’t find any pictures of it via Google, but here’s a similar toy that’s a bank. Instead of turning it on with a switch, you put a penny in a cradle, and the hand comes out and snatches it.
Back in the late 80′s I often rented Fords with something similar to this machine. There was a lever in the center console. When you pulled the lever, a light flashed to tell you to push it back. (Imagine my disappointment to discover that the lever actually had another function, releasing automatic shoulder belts after a crash.)