Home alarm wiring
I am replacing an exterior steel door that has a recessed magnetic door contact for an old First Alert home security system. The contact in the door frame does not have exposed leads. Can I just cut/splice the wires without damaging the system? Of course, it's a Sunday so tech support is closed and there is nothing helpful on their website.
Yes, you can cut the leads. For as long as they are not reconnected, that Zone will indicate a "Trouble".

Just like it did when you opened the door.

Each (hard-wired) Zone in an alarm system consists of a low voltage wire out from the panel to the switch, 

and a wire back from the switch to a different terminal in the panel. 

Somewhere in that loop, usually inside the panel on the return leg, is a resistor.

The panel monitors the voltage drop (because of the resistor) between the line out and the line in.

Opening the switch or cutting the wire breaks the connection in the loop, and tells the panel that the Zone is "in Trouble".

When you reconnect the wires, the Zone will go back to normal.
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Thanks, Barnowl. Anything special about splicing home alarm wires? I would plan to use crimp connectors with heat shrink wrap since it's an exterior wall.
(06-07-2020, 11:32 AM)RichK Wrote: Thanks, Barnowl.  Anything special about splicing home alarm wires?  I would plan to use crimp connectors with heat shrink wrap since it's an exterior wall.

Not really.

Some installers crimp/heat shrink like you, but I've seen some solder and heat shrink. 

Either way is fine IMHO.
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Great. Thanks your your help!
Jumper the connections and avoid the “trouble” code.
The resistor should be at the door sensor (reed switch) because a crafty thief could just jumper the wires and the panel would not see a change.  Of course the thief would have to get inside to do the jumper job...so much for details.

The reality is that no one picks the locks and jumpers the sensor.  They break a window and open the door, grab your TV, jewelry and anything else that they can get in a minute or two and they are gone.  The PD is not speeding to your home because they have a batch of other false alarms especially now that there are so many do-it yourself systems. No I am not in the alarm business but I know someone who is.

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