The problem is that the Coastal mod only does half what I want. (More pressingly, it does the less important half.)
It makes the doors auto-lock when the vehicle moves faster than 15 mph. That is nice and all, but it's not the important auto-lock.
I want the car to lock itself a certain period of time after I walk away from it. (Say, 3 minutes after I get the SE/SS fob out of range.) This way, when my wife forgets to lock the door (as she does all too often, since the never thinks about unlocking it,) the car will lock itself in a few minutes. To me, 3 minutes seems like a good number, because it's soon enough that unless someone was waiting for you to leave, it would be soon enough; and long enough that you could run in the house to grab something and it would still be unlocked for you. (Maybe make it settable by doing a funky combo of stuff like you do to set current options.) Of course, like the current SE/SS button arrangement, I wouldn't want it to lock if the key was left in. But more pressingly, I'd want it to beep at you if you walk away with the key in, the same way it does now if you walk away with the key while it's running.