Put your cinder blocks away, those wheels aren't worth anything.
From the submitter:
So I get up today and the kids are up before me watching TV. That's fine, it Sunday, got to sleep in, figured I go check my email and puts around online for a few. Later I go into the living room, to turn the TV so I can start watching Game highlights before the Super Bowl, but can not find the remote. I mean I searched everywhere. The usual places... In the couch cushions, under the couch, behind the couch and behind the TV.... nowhere to be found.
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!