My home has a central alarm system with keypad and every door and window set up with a sensor except for 1.

This 1 sensor was removed when the previous owners replaced the frame, and it keeps the entire system from being able to work.

I asked a local company for a quote and it was a few hundred dollars because they claimed they would have to replace the keypad and some other things. (they also claimed I had to buy monitoring, which seemed very odd, and sketchy)

I looked at the main circuits and could not find a brand name, so I am at a loss for which it is, which makes this task even harder.

So my question is:

What steps should I take to figure out which alarm model I have how to go about installing the sensor?

  • I would look to the keypads to determine make/model. Generally these are sold as a kit.
    – jamesson
    Dec 6, 2011 at 4:56

3 Answers 3


It's surprising not to have a brand name visible, either on keypads or the main system. I will say it is possible that your system is very outdated, and so the alarm company basically doesn't want to touch it (rightfully so), they just want to put in something modern which they know they can support if it breaks.

You should have a control system somewhere. Often these are a metal box that opens and has a circuit board inside. There should be a model number or name on that, and if not, posting a picture would help.

enter image description here

If there is a circuit board like this, it is possible the model/name is printed on the reverse side, as they actually sell the box separately from the circuit board -- the installer mounts it at install time. You'd have to remove the circuit board in order to check this (cut the power, and be careful not to damage the board -- including being careful of static).

Aside from that, there are three general ways to go about fixing the problem.

  • Install the missing door sensor

Installing the sensor may or may not be easy. If you have another door sensor, you can verify that you're getting the same thing (usually just a NC magnetic contact sensor, like these):

surface mount door sensor recessed door sensor

  • Short out the door sensor wire

You may be able to short out the door sensor. There is a very small chance that this won't work, if it requires a resistor to terminate, but that is not common on door circuits. Of course, this door won't be alarmed if you do that. It also means you need to find that wire, somewhere. You could do it at the panel, as well.

  • Remove the door sensor circuit

This means re-programming the system to not use this circuit. It definitely requires finding the model, and then figuring out how to program the system. Sometimes this can be done through (at best) cryptic button sequences, other times it needs PC software and a (sometimes special) cable.

  • 2
    +1, these types of sensors are dead simple in construction. Sensors basically come down to NO (normally open) or NC (normally closed). Since it's not working in an open state (no circuit), you need a NC sensor. You can confirm that by shorting (connecting) the two wires together. Dec 6, 2011 at 1:23

Most sensors are generally universal, if it's missing entirely, you could take one off of your other doors and bring it to your local home store and see if you can find a similar or matching one. Most door sensors are just magnetic switches that close a circuit loop when secured.

One thing you might be able to do is to twist the two wires together, completing the circuit, and see if you can arm the system. The down side to this is that that door won't be protected, but the rest will.


Door contacts are typically non-proprietary. Meaning, it is a simple contact with a reed switch that just changes states when a magnet is close to the contact. This means that you can use anybody's wired door contacts on anybody's control panel. There are two terminal inputs on each zone of your control panel for each of the wires to be terminated.

With regards to the make and model of your control panel: On the inside of the can there is typically a riser/diagram of the panel. This has detailed information on wiring, zone descriptions etc. MOST of the time, the make and model is on the BOTTOM of this sticker on the inside of the panel.

If you decide that it is too cumbersome to run the wire from your control panel to your door, and then drill out the door for the contact to be recessed, you could consider installing a wireless RF receiver to take advantage of wireless contacts that most manufactures offer.

Hope this helps!

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