Tech Forum

There are several reasons an Arduino hobby type PIR is not a good substitute for a commercial PIR motion sensor.

1. You will need to step down the 12V to 5V with a voltage regulator. Coincidentally page 78 of the July 2015 N&V Tech Forum has answers for a 5V regulator question .
2. You will need to add a 5V relay from the TTL output of your Arduino PIR so that you can provide floating form C (COM and NC) contacts for Alarm COM and ALARM NC. Normally the ALARM contacts are closed unless an alarm condition is sensed. All sensors and switches in the ALARM loop are wired in series in a burglar alarm. Color code may vary, but in my experience a red and a black wire were used. You should pay attention to the colors used in your system.
3. Unlike a commercial PIR, the Arduino PIR does not have a optical shield and/or shutters to adjust the beam width. As such, it will have a broader sensitivity and be susceptible to false alarms from moving persons or objects outside windows or pets inside. Additionally, it may be blinded from ambient light sources.
4. The terminals marked TAMP 1 and TAMP 2 are tamper switch connections. Normally the tamper circuit is closed unless the sensor case is opened. In my experience a white and green wire were used for tamper circuits. Yours may differ. If the tamper switch is opened in a commercial alarm system, a supervisory signal is sent to the alarm office and a technician is sent to inspect the system. This is to prevent a would be burglar from opening the sensor and tampering with wires or placing tape over the PIR sensor. In a residential alarm system, a trouble light will appear locally at the control panel. With the above information, you can make the Arduino PIR function, however the possibility for false alarms will be much greater unless you are willing to spend the time constructing a proper light shield.

The $89 quoted by your alarm company sounds fair, and is an even better deal if they install it for that price. If you are under contract for alarm reporting to the central office, modification of the system may create problems with the agreement. You may be able to find an equivalent commercial sensor on E-Bay for a good price if you insist on replacing it. Personally I would stick with a commercial PIR for this application.

You only need to connect four wires for a burglar alarm motion detector to work properly. “GND” and “12V” are voltage for the motion detector - 12V is the positive, GND is the negative. “ALARM COM” and “ALARM NC” connect to the zone input on your burglar alarm panel. Typically, there is no need for polarity because this is a simple switch - with no motion in the area the switch is closed, motion is detected the switch opens.

“TAMP1” and “TAMP2” are connected to a mircoswitch within the motion detector housing that activates your alarm if someone were to remove the cover - called a “tamper.” If anything is connected to these terminals, you can simply twist the wires together, complete the circuit, and cap them off. It is not necessary to utilize the tamper feature and is often not recommended.

But, I would avoid any type of “inexpensive” replacements for your alarm system motion detector. One of the major sources of false alarms in burglar alarm systems tends to be the motion detector. Installing a motion detector not specifically designed for burglar alarm use may end up causing false alarms with your system and depending on your jurisdiction, fines from the local police department from the dispatching of those false alarms. Most burglar alarm motion detectors are designed to limit false triggers - so I would suggest going that route.

I did a quick search and could find a reliable motion detector listed for burglar alarm use for $25. Easy enough to replace yourself, just make sure you seal up any penetrations in the housing where the wire and screws go through. Spiders love to make homes in these and that will also cause false alarms.

Alternately, $89 may not be a bad price for your alarm company to replace the detector if that includes the labor. Nobody wants to work for free after all! Plus you can get them to quickly check your system to make sure it is communicating properly to your monitoring company and everything is working correctly.

TAMP1 and TAMP2 are the tamper contacts. They are normally closed as long as the device is not being tampered with. They are just ‘dry’ contacts and could be connected to the Arduino.