ADT Alarm (or any alarm for that matter)
Your 'ADT' alarm is able to transmit a signal to a central monitoring station via your phone line using a pre-determined digital code to a specialized receiver/computer interface. To oversimplify it, its like a FAX machine's signal if you have ever picked up the phone when it was sending/receiving a FAX. All you hear is a series of beeps and screeching. If you programmed your neighbor's, mom&dad's, etc. phone number into the alarm and it sent an alarm to them, they would just utter a few choice words (ie. "What the H@ll is that?") and hang up.
Radio Shack sells a 'Voice dialer' which you can connect to the bell output of your alarm. It will dial up to 3 pre-programmed telephone numbers (ie. mom&dad, the neighbor and your cell phone) and deliver a pre-recorded message (ie. "Joe's alarm is going off please check it out!").
I have not used one myself, but I imagine it comes with excellent documentation on how to hook it to any generic alarm system.
You will either hook it directly to the "BELL OUTPUT" (observing polarity!) or you will need to purchase an additional 12 volt relay to provide a non- powered (dry contact) switch to the dialer. Consult the well written documentation which accompanies the dialer.
Make sure that you still have an alarm permit filed with the local authorities. If
anyone calls the police when your alarm sounds you can be subject to a hefty fine if you do not have a permit, even if they attend and find a bad guy in your kitchen eating your cookies!