The Arduino board has been the engine of many wild and wacky projects over the years, from bakery tweeting
to various musical instruments
. For its next trick, our man Steve Hoefer has taken his microcontroller and, along with a piezoelectric speaker, a gear reduction motor, and some PVC pipe, programmed it to listen for a preset sequence of knocks -- a secret knock, if you will -- and unlock the deadbolt upon hearing the right combination. Although this might not be the security system you want to put in place for your home, this definitely looks like a fun weekend project. Check out the read link for instructions and schematics, but not before you see the video of the thing in action. It's after the break.