First of all, my condolences. I used to work on those things in the mid-90's and they were obsolete then. I'm afraid the most work I did with them in the last 20 years is replacing them with a mainstream brand that is DIY-friendly. The AT&T is not DIY-friendly, and finding replacement parts will be very difficult if not impossible.
I'll do what I can to help, but my memory is pretty fuzzy after 20 years.
I hate to be the bearer of bad tidings, but AT&T's "System 8000" was kind of a huge joke in the alarm industry even when it was new. Back in the 80's there was a boom in the alarm business and everybody and his dog were getting into the business. (I even had to work on a Mitsubishi atrocity--true story.) When AT&T came out with their System 8000, it's as if they didn't even glance at what the current state of the art was, and just re-invented the wheel, but their final product was obsolete before it came off the production line--it was more like something out of the 70's than the 80's, except that it really wasn't like
anything else in the industry. They just sort if ignored how everybody else was doing it.
That being said--if you really want to hang onto your System 8000 and try to make it work, here's a link to the manual:
http://www.ronstultz.com/knowledge/...ome Security System - INSTALLATION MANUAL.pdf
You'll notice that the Central Controller's model number is 8720--the system as a whole is called the "8000 System".
You said the system goes into alarm "...every time I open the door to my house..." Does your house have more than one entry/exit door? Is this happening with all the doors in your house, or is it just with one door?
I remember that the Sys 8000 door/keypad units had a peculiar protocol that allowed the user to temporarily bypass (not disarm) its particular door long enough to leave after arming, but exiting by another door would trip the alarm.
Another critical question: Have you been using this system for awhile (in which case, you probably aren't being confused about how to use it, as a user of any
other system would be), or is it in a house that you just moved into, or what? Was it working properly up until your current problem?
As I said, I haven't worked on those systems in about 20 years, but here's a link to a DIY alarm system site where you might find someone with more recent experience:
http://www.shieldlab.com/forum/index.php/board,2.0.html
