Instructables user cbaabc73 came up with a cheap and easy way to turn off outlets when you aren't using them. He built it after noticing his wife kept leaving the curling iron plugged, which can be extremely dangerous. This DIY project takes only basic tools without the use of soldering.
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!