You can leave your keys at home with this clever hack by Billy Chasen, who rigged up his deadbolt to a Propeller-based Spinneret Web Server. Using an SMS gateway called Twilio, he can open and close the lock by tapping out a quick text message. Not only that, but the system also responds to acknowledge his request. For security, there's a whitelist of permitted senders.
It's an awesome project, but I hope for Billy's sake that his deadbolt doesn't go rogue and start texting up all his deadbolt friends. "R U unlocked right now?"