By hs_pfroum
PIR stands for Passive Infrared — the most common and most reliable type of motion detector used in home security systems. Every major wireless alarm system includes at least one PIR in its starter kit, and for good reason: a single well-placed PIR can cover more of your home than four or five door sensors. Here is everything you need to know about how to use them effectively.
How PIR Motion Detectors Work
A PIR sensor detects changes in infrared radiation — in practice, the heat signatures of warm bodies moving through its detection zone. The sensor does not emit anything; it only detects changes in incoming infrared energy. When a person walks into the detection zone, their body temperature (around 37°C) contrasts with the ambient room temperature and the sensor registers the change, triggering the alarm.
PIR detectors do not detect motion directly — they detect changes in heat. This is why they can be confused by heating vents, radiators, and large pets, and why well-designed “pet-immune” PIRs calibrate their sensitivity to ignore heat signatures below a specific size threshold.
Placement: Where a PIR Makes the Biggest Difference
A PIR mounted in the corner of a room at 2–2.4m height pointing diagonally across the space covers the maximum area. The typical detection range of a residential PIR is 10–12m with a 90–110° field of view. A single PIR in the corner of a hallway facing the front door covers both the entry from the door and the approach through the hallway — two key positions in one sensor.
Common effective PIR positions: corner of the main hallway, top of the staircase covering the stairs and landing, corner of the main living room, and garage interior facing the main door.
Pet-Immune PIR: Does It Work?
Pet-immune PIRs reduce false alerts from animals by using dual-element sensors calibrated to ignore small heat signatures. Most pet-immune sensors claim immunity for pets up to 25kg. In practice, the accuracy depends heavily on placement. A dog that stands up on its hind legs, sits on furniture, or passes close to the sensor at an unexpected angle can still trigger the alarm. Pet immunity works best when sensors are mounted correctly at the right height and the pet’s normal movement is below the detection threshold angle.
Compatibility With Alarm Systems
Most wireless PIR sensors communicate via Z-Wave, Zigbee, or proprietary RF. Ring Alarm, SimpliSafe, Yale Smart Living, and Reolink Home Alarm all use proprietary wireless protocols for their own sensors but accept third-party sensors via Z-Wave on compatible base stations. Always check ecosystem compatibility before purchasing additional sensors. See our full alarm system and sensor guide here. Browse all security sensor articles here.
