The Knock Clock is pretty ingenious, what with its knock-knock get the time action, but I can't help but feel sad for the little woodpecker trapped within. Not even a single air hole. How long does he have?
I'd say about three of four knocks worth. Until that time, let's close this post out with the specifics on this simple little clock.
Created by three Copenhagen Institute of Interaction Design students in about 48 hours for a competition, the clock tells you the time of day (to the quarter hour) after you knock on the top twice. Placing a hand over the sensor near the corner sets the alarm function. The alarm function also features—you guessed it—more knocking. [Adafruit via MAKE]