I'm wondering about security here, and perhaps your son should too given his profession. Having the phone try to be smart about lock/unlock based on location is simple on the surface, but some of the edge cases worry me. Example: what should the car do if it can't get a GPS fix? I would imagine it should assume the worst and lock, which seems sensible. Ok, fine. You get used to the feature NOT locking your car at home. Then one day the weather or some such anomaly messes up GPS for a few minutes, and the care decides its not sure where it is even though it is safe at home and locks. With your phone in it. Oops.
Contrived perhaps, but the more complex you make locking options, the more ways there are for them to do the wrong thing. That's why the best security systems are always the simplest; complexity, especially complexity for the sake of convenience, is the enemy of security,