GateKeeper Automatic PC/Mac Lock

$24.99 from Amazon >

GateKeeper is a small keyfob that automatically locks your computer when you walk away from it and unlocks it when you return. The GK's USB Lock plugs into a PC or Mac port, users carry its Key on their person, and the 2 components link via Bluetooth. They can be set to respond to proximities between 0 and 100 feet. In other words, if your desired range is 50 feet, GateKeeper will auto-lock your computer when you walk more than 50 feet away from it, and auto-unlock it when you meander over the threshold towards it.