Ripping a page straight from James Bond, enterprising hacker sprite_tm built this knock-activated door unlocker to help out a friend who wanted to keep his access to a room in his apartment building a secret. The system listens for a particular pattern of knocks speakeasy style and triggers a decidedly low-tech unlock mechanism when you enter the right knock-code -- it winds a rubber band around the lock handle. We're not certain if we buy the backstory here (what happens when the landlord sees a giant motor gaffer-taped to the inside of the door?) but the idea is pretty sweet, and we're even thinking of a mod to make the door scream "TWO BIIIIIIIITS" when we knock "Shave and a Haircut".
[Via Hack A Day