I tell you what Gobadgrs... we live in a very nice subdivision - quiet, peaceful, you name it. But sure as sh!t, some dickwad smashed my driver's side window and opened my garage via the garage door opener last summer. The scariest part was my wife & I slept through the entire thing, INCLUDING when a police officer was pounding on our door at 5am to let us know that we had been broken into. We got an alarm system installed about a week later. Motion detectors in the garage and basement, and on the main floor also when we're away. I'll never look back. It really does bring peace of mind.
That ADT system sounds a little more upscale than ours, but the sky's the limit with these systems.
With ours, if it goes off, the phone is ringing within a minute - reps from the company asking if everything is ok, asking for the password, etc.