This little guy had a life-threatening illness and needed his leg amputated. Luckily, the doctors at Washington State University's veterinarian school came up with a plan that even a 12-year-old tortoise's HMO covered.
Steve Hoefer at Grathio labs shows off his Arduino based door opener, which responds to knocks on the door bye timing the gaps between the sounds. If the gap matches the programmed knock, it unlocks. Let's never use keys again!
Know a little bit about Arduino and care to make your own? Check out his Instructables post!