Sure you can go crazy and drop a few hundred bucks
on a high-tech door lock, or you can follow the lead of the folks from Makers Local 256 and build this USB-authenticated deadbolt, which should set you back just $60 -- or no doubt less if you can scavenge up some spare parts. The setup is based on Arduino's
slightly lesser known cousin the Freeduino, and effectively turns any standard USB thumb drive into a key, which can be just as easily lost or misplaced as a regular key but not as easily duplicated. What's more, it's not the data on the drive that gets read by the lock, but rather the serial number on a chip, which leaves the rest of the drive free for you to use as you please. Head on past the break to check it out in action.