PIR, Dual-Tech, and Microwave: Motion Detector Types Explained

Passive Infrared (PIR): The Standard

The vast majority of residential motion detectors use Passive Infrared (PIR) technology. PIR detectors don't emit anything — they passively sense changes in infrared radiation across their field of view. Humans are warm-blooded and emit infrared energy; when a person moves through the detector's detection pattern, the change in the infrared signature across adjacent detection zones triggers the sensor.

PIR detectors are highly reliable for human detection, have low power consumption, and generate minimal false alarms in controlled environments. Their limitation: they respond to any infrared source, not just humans. Hot air vents, sunlight streaming through windows, and pets can all cause false triggers.

PIR Detection Patterns

Most PIR detectors have a coverage pattern of 90° horizontal by approximately 40° vertical, covering a room-sized area to a depth of 30–40 feet. Some models offer wide-angle 180° coverage. The detector sees movement across its detection "curtains" (adjacent infrared-sensitive zones) — not movement directly toward or away from it. This is why placing a PIR detector at the end of a hallway (where someone would walk directly toward it) is less effective than placing it at a corner to capture cross-movement.

Microwave: Motion by Doppler Radar

Microwave detectors emit low-power radar pulses and measure changes in the reflected signal. When something moves within the detection zone, the reflected frequency shifts (the Doppler effect) and triggers the alarm. Microwave detectors can see through walls and glass — which is both an advantage and a disadvantage.

Advantages: Works in complete darkness, unaffected by temperature changes, can detect very slow movement that PIR misses (PIR requires a relatively fast change to trigger reliably).

Disadvantages: Can be triggered by movement outside the room through thin walls. More prone to false alarms from HVAC fans, ceiling fans, and vibrating surfaces. Generally more expensive than PIR. Used alone, they're not common in residential applications — they shine in combination.

Dual-Technology (PIR + Microwave): The False-Alarm Solution

Dual-tech detectors combine PIR and microwave sensors in one housing. The alarm only triggers when both technologies detect motion simultaneously. This dramatically reduces false alarms: a sunbeam might fool the PIR, but won't fool the microwave. A ceiling fan might register on microwave, but won't have an infrared signature.

Dual-tech is the right choice for spaces with known false alarm challenges:

• Rooms with south or west-facing windows that get direct afternoon sun
• Spaces with HVAC vents that create air movement
• Garages with outdoor temperature swings that affect infrared background
• Businesses where ceiling fans or industrial equipment creates constant environmental noise

The trade-off: dual-tech detectors are less sensitive than single-technology PIR because both sensors must agree. In a cold garage, a slow-moving intruder might not register a large enough infrared change to trigger the PIR half of the sensor. For most interior residential spaces, standard PIR is sufficient. Dual-tech earns its cost in challenging environments.

Pet-Immune PIR: A Special Case

Pet-immune PIR detectors use a combination of detection zone masking and weight estimation (via multiple detection layers at different heights) to ignore animals under a specified weight — typically 40–80 lbs depending on the model. The detector is effectively blind to movement at floor level, which is where pets move, while remaining sensitive at human height.

Pet-immune detectors are not foolproof. A large dog (over 80 lbs), a cat jumping on furniture, or a small child can still trigger them. They're best understood as false-alarm-reduction devices, not absolute pet-bypass systems. If pets are present, installing perimeter sensors on doors and windows and using motion as secondary protection is more reliable than depending entirely on pet-immune motion detectors.

Placement Strategy by Room Type