I have ADT as well. I just bought my house a little over a month ago, so I've not had the service long. Though I can say that the response time is great when I forgot to deactivate the alarm. They called right away!
I happen to have three old timers in my "hood."They can tell me what time of the morning I get up to #&^%.
Sometimes look around at your local companies and see what packages they have to offer.
One company around here will do drive by's when you ask, I know because of the construction jobs we hire them to patrol.
We're using Monotronics. had the system for about 4 years now and it works great.My shop was broken into once and the p[olice caught the guys in the act of loading up my tools. I don't use an outside siren. I would rather catch them then scare em off. LOL
I think most of the well known monitoring places are all using very similar equipment now. My experience is that if you post the signs, it won't stop people from breaking in. They just limit their time inside the house so they don't get caught. They know that a lot of monitoring companies call first and check before they actually send the police.
I have a dog... and guns. (I had trouble with a neighbor once, and Police came and took my guns away for awhile, thinking I might shoot him...his dog was terrorizing my kids! I went after the dog with a gun)... Cops said it looked like Ft Apache with all my ...ahem... items of interest
Neighbors all looked on while they took all the armaments away...
I actually use a home grown system of sorts...I am in to home automation ...x10 stuff and I have an x10 security center attached to all the windows and doors and an added ear splitting additional horn I also have a few camras around the house. the x10 security cent does not have a service but it has a dialer the will call up to 4 numbers that I program in to it and my wife work about a mile away from home so it dials her and my folke that live about a mile away as well. No one has broken in yet but I did have a real good pic of a kid stealing a christmas Decoration. he was a neighborhood kid so I printed out the pic and gave it to his mom.. he never stole anything again.