The TI Chronos has been a bit of a hackers darling recently, but this has to be the coolest application of it I’ve seen so far. Rather then getting an RFID tag embedded in your hand, program your watch to use a pre-programmed combination of taps to activate the wireless door locking system.
The inventor created this locking system using the TI development kit, some basic electronics, and the Chronos watch. The watch uses a 128 bit AES key encryption, and requires that you know the pre-programmed tap code before it will open the door. This is more secure then RFID, which just opens based on proximity. I love this project, the only potential issue I could see would be someone mugging you and stealing your watch, leaving you unable to open your door (unless you have a key with you).