This system I don;t think has foiled any would be home invaders (as far as I know) but it did alert me to the cat picking the door open and trying to escape into the night. The noise the alarm emits is very shrill and loud and would scare any burgular (or cat) half to death.
I did have a problem with ADT in terms of being overbilled at one time, but they pointed out they had gone to a quarterly billing system of which I was unaware. I think it is worth it to get ADT Home security system as it will reduce your homeowners insurance bill. by about 20 percent and give you peace of mind.