Tether – Locks your Mac when you walk away and unlocks it when you return (hellotether.com)

Car lock radio devices had a man-in-the-middle attack vector where a repeater could be set up by the car, and a roamer with another would walk thru the mall until they got close to you by accident. Then your car would unlock.

I imagine this is more sophisticated? Geolocation is hard to forge; each device is talking to the internet and not just pinging radio.