They're very expensive, and have horrible customer service and very terrible internal processes. We will be switching as soon as our contract is up.
Firstly, they do not give you a customer bill - even after requesting. The systems are literally not capable of giving you a copy of your bill so you know what they are charging you for, which seems absolutely absurd.
Secondly, we have had the system for only a few months and have had so many problems with fake alarms. On one instance, we got a notification saying our door was left open. They didn't call us for three hours. It ended up being a fake alarm, but what if it was a real one? We have two dogs at home and they could have run away - and would ADT really have done NOTHING for three hours? What are we paying them for?
To say we are disappointed with ADT is an understatement. Please save yourself the hassle and do not sign up for their services.