Because ADT uses multiple contractors- not all services is consistent. Whenever I had issues with the system, it would take multiple departments in order to fix. When my alarm would go off- I wouldn't even get a call 1 out of 2 times! One time in particular, I had wanted to upgrade my system- and I was told that I couldn't because a third party had installed. I was mystified- how was it I had an ADT bill every month, and spoke to an ADT representative and they couldn't make the switch? Multiple departments later- they couldn't figure it out. How does a home security system operate when they have such a lack of internal communication?
Ultimately, after 8 years of somewhat questionable service- I switched to a new home security provider- who was able to upgrade to new and so much better system with a more reliable company that provided digital cameras, smoke monitoring etc.
When you have a choice in home security providers- buyer beware!