I've had a mixed experience with ADT. When the alarm triggers we usually get a very quick call from ADT.
However our house was recently broken into during the day time and unfortunately I did not turn on the ADT alarm. However, the intruder knocked loose our front door sensor. I called ADT to come and fix. They said they would send a technician the next day from 12-4pm. Waited all day then they called at 4:30pm saying they could not come.
So I rebooked with them the next day from 2-6pm the next day. The tech came at 7pm. I thought they would send the tech first thing after missing the call the day before but I was wrong and waited another 5 hours.
The tech who came was excellent, but I was disappointed this is how they would treat a long-time and loyal customer. I'm hoping I'm treated better as I look at a newer alarm system, or I'll switch to another company. ADT like a lot of big American companies seems to put a low priority on customer service, then wonder why they lose customers to competitors with excellent service.