This charming Knock Clock was made by three Copenhagen Institute of Interaction Design students for a 48-hour design project. When you knock on the top of this minimalistic wooden box, it knocks back the time of day (to the nearest quarter hour). It even has a basic alarm function, which—naturally—is set by knocking as well. [via Adafruit]

Update: Check out the interior of the Knock Clock here.

More:

• Secret Knock Gumball Machine
• Secret knock-detecting workshop door
• A Clock That Eats Flies
• LED Pong clock
• Clock Built for Extraterrestrial Travelers