ADT is the biggest scumbag alarm company of them all. They spend all their money on yard signs and polished commercials.
When I bought my house, it had an ADT locked Vista 20p Panel that was so badly done I had to redo the whole thing. It had 8 zones, yet I have 24 points of protection? I called to ask them to release it for me so I could redo the system and monitor it myself, they laughed at me. So I yanked it, bought a fresh 20P, a TC2 compatible chip, 2 zone expanders (now at 24 zones), some fresh smokes and motions detectors, a cellular radio and wired it all up. I knew NOTHING of alarms at the time, I just googled questions I had and got it done.
I have Geoarm doing the monitoring, and with one phone call they initiated the system and got connected to it. I did all the wiring, zone naming and programming and all the other local stuff. I can add sensors, rename zones, modify or expand the system all I want (and I do every now and then) and I don't have to call anybody.
I have full 24 zone remote ap control, completely monitored for police and fire, and pay $27 a month. ADT wanted over $50. I inquired once about video surveillance and almost threw up on the phone. It was some insane monthly numbers for 480p cloud cameras. The best they had. LMFAO GTFO.
Anybody that has any sort of DIY skill should go this route. Give yourself the freedom. ADT holds you and your equipment hostage.
I'd try to talk that owner out of it, just present the facts in a respectful way. ADT is for ignorant consumers. Almost any local independent alarm contractor would be better.