Motion Sensors, or more specifically passive infrared (PIR) motion sensors, use infrared light to detect large moving objects (like a person) in the interior of your home. These are usually mounted in the corner of a room near the ceiling in living areas of your home. Most motion sensors installed for security systems operate on 12V DC power and are connected to four wires: two for power and two for the motion signal. Red and black wires are usually the positive and negative power wires respectively. The other pair of wires could be any color and carry the motion detection signal. These operate like a Normally Closed (NC) switch: When no motion is detected, the signal circuit is closed. When motion is detected,the signal circuit is open.
1. Identify Wires for your Motion Sensor
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If you’re re-wiring an existing alarm system, your motion sensor power wires (red & black wires) are most likely already connected to the power output of your alarm panel. If these are working correctly, you should see an indicator light on the motion sensor when it detects your motion. Leave the power wires connected and follow the wiring instructions below for motion sensors with external power.
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The other pair of wires for the motion detection signal are most likely connected to one of the zone inputs on your existing alarm panel. They may be wired with end-of-line resistors at the alarm panel. Disconnect this pair of wires from your existing alarm and remove and discard the resistors (or save them for a different project).
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If you’re wiring a new motion sensor, or one without an existing power, follow the wiring instructions below for motion sensors without external power.