Old thread but I've got an alarm question so thought I'd start it again.

My alarm just went off while car parked in the garage and locked. (Leaving town so locked the car.) When I opened car door the alarm didn't go off! I had to start the car before the alarm went off. Now I'm afraid to lock the car for fear the alarm will go off while I'm gone and neighbors will lynch me for the disturbance!

Now, what caused alarm of car in garage to go off? Why didn't unlocking the door shut off the alarm? Did I do something wrong?

Thanks

John