Slow service, terrible accounts, zero support.
Security itself? 2/5
I had the police at my door dealing with vagrants 15 mins quicker than the ADT team I paid for at 3am... and I phoned the police nearly 10 mins after ADT... At least they showed up I guess.

Accounts departments 1/5
I cancelled my account with ADT in Feb 2019 as I was moving in April... I received a call from my father today (Sep 2020) asking me about an outstanding ADT account and that he was liable for payment on my behalf... Apparently they did not debit my account for the last month and NOT A SINGLE PERSON tried to contact me about it... they handed over my account to debt collectors in Dec 2019.. who then waited 9 months to do anything about it and the first thing they did was not contact me. no they contact my father...

I was a sceptic when I signed up for the services to begin with. for the most part it was useless... the hardware they came to replace didn't really work, the service was slow and if I had to actually rely on them in an emergency I would have probably not been around to post this statement. 

If your only option is ADT? Get a dog instead. 