My experience with ADT was not through their service per se, but actually by one of their salesmen. One of them rang my bell tonight, and was probably one of the pushiest salespersons that I have experienced in a while. He just would not listen to no, and after being polite for a while, I literally had to close the door on him. This pretty made up my decision to never become a customer to ADT all by itself, but after seeing the experiences many other people here on Yelp, I can see that I made the right decision.
I was also certainly not the only person to have this kind of door-to-door encounter with an ADT guy. I went to Google and typed in "pushy ADT", and the word "salesman" came up automatically. Yup. Sorry dude, if you "come back later", like you said when I closed my door, the answer will still be no.