Here is a bit more information on security systems, from Richard Fitzgerald
in Tulsa, OK. Richard is not a contributor to RCM, but I "drew" on him for
more information.

Bob Swinney

Richard Sez:

Can't remember the name, matter-of-fact I just threw it out during the great
dumpster filling of 2003. Most of the current burgler alarm equipment is
made by ADEMCO. Most of the home security companies just have their name
stuck on it. Most modern systems are modem based and dial into the
monitoring centers computer and dumps a numerical code identifying the
location and type of alarm. Some of the better alarms monitor the phone
line for -48V and in the event they loose the voltage they will dial in via
a cellphone type of connection. Used to most of the central staiton
monitoring was done over a leased pair with a 10ma. current loop, the
monitor panel had a under current and over current relay for status. You
probably remember those in a lot of the small town police stations usually a
small panel with several meters with a couple of lights, it was made by
ADEMCO. In larger towns (Tulsa) they would use a series loop that would
take in as many as 20 businesses in a large series loop called a McCullah
loop. At the central station they had a pen register that moved in relation
to a break in the circuit. Each business had a closed loop for the alarm
and a relay with a code wheel that was in series with the alarm loop. If
you had a premises trip it would cycle the code wheel and the cestral
station would mark the code of opens and closes on a pull paper looked a lot
like tty paper, the operator would read the code and dispatch to the
location bases upon the code. Digital telco CO and interoffice fiber trunks
has did away with these type s of alarms