As long as you consistently lock your car when you get out and walk away from it (when your mom's not driving it, anyway) the car should remind you to shut it off before you leave it. If you try to lock it while it's still on (and I _have_ done this, lol.. sometimes it's so easy to lose track of whether it's on or off!) it will beep loudly at you and if I remember right, it won't lock.

On the other hand one night I actually left my car on while I ran inside to grab/do something, figuring at least nobody will be able to tell it's running!