Technical Foundation
What Is a Motion Sensor?
A motion sensor detects the presence or movement of a person or object in its coverage zone and switches an output — commonly used to control lighting, trigger security alarms, or signal automation equipment. Passive infrared (PIR) sensors detect changes in infrared heat radiation as a warm body moves across the sensor's field of view, offering reliable line-of-sight detection at low cost but no ability to sense motion through walls or around obstructions.
Microwave and ultrasonic sensors emit energy and measure the Doppler shift of the reflected signal caused by motion, detecting through thin partitions and around obstacles that block PIR, but at higher cost and greater susceptibility to false triggers from HVAC airflow or moving equipment. Dual-technology sensors combine PIR and microwave/ultrasonic detection, requiring both technologies to confirm motion simultaneously before triggering, which significantly reduces false triggers in demanding lighting-control applications at the cost of occasionally missing very subtle motion.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Detection Technology | PIR, microwave, ultrasonic, or dual-technology | Determines detection reliability, false-trigger rate and whether detection works through obstructions |
| Coverage Pattern & Range | Field of view angle and maximum detection distance | Must match the room geometry — a narrow corridor sensor pattern won't adequately cover an open floor area |
| Mounting Type | Ceiling, wall, corner | Determines coverage geometry achievable and installation location relative to the monitored area |
| Output Type | Relay contact, 0-10V dimming, low-voltage switching | Must match the lighting control or automation system's input requirements |
| Environmental Rating | Indoor vs. outdoor (IP65/IP66), temperature range | Outdoor and washdown sensors need ingress protection and wider temperature tolerance than standard indoor units |
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Applications
Where Motion Sensors Get Used
Motion sensors are specified wherever automatic detection of presence or movement drives a lighting, security or automation response.
Commercial Lighting Control
Occupancy sensors switching or dimming lighting in offices, restrooms and warehouses to reduce energy consumption per code requirements.
Security & Perimeter Detection
Outdoor motion sensors triggering alarms, cameras or floodlights around building perimeters and restricted areas.
Warehouse & Distribution Automation
Motion and presence sensors triggering conveyor stops, dock lighting or safety interlocks in material handling systems.
Parking Garages & Stairwells
Dual-technology sensors reliably detecting occupancy in spaces prone to false triggers from airflow or reflective surfaces.
HVAC & Building Automation
Occupancy input feeding building management systems to adjust ventilation and temperature setpoints based on space usage.
Industrial Machine Safeguarding
Presence-sensing devices integrated into automation logic to detect personnel near moving equipment zones.
FAQ
Motion Sensors Questions, Answered
What's the difference between PIR and microwave motion sensors?
PIR sensors detect the infrared heat signature of a moving warm body and require direct line of sight, making them reliable and low-cost but blind to motion behind obstructions. Microwave sensors emit RF energy and detect the Doppler shift from motion, penetrating thin walls and glass and covering wider areas, but are more prone to false triggers from HVAC airflow, moving machinery, or even motion in an adjacent room.
Why choose a dual-technology sensor over a single-technology one?
A dual-technology sensor requires both its PIR and microwave/ultrasonic elements to detect motion simultaneously before triggering, dramatically cutting false triggers compared to either technology alone — useful in spaces like stairwells, restrooms, or open warehouses where nuisance triggers from airflow or reflections are common with single-technology sensors.
How do I size the coverage area for a ceiling-mount occupancy sensor?
Check the manufacturer's coverage diagram for the specific mounting height, since detection range and pattern shrink or distort outside the sensor's rated mounting height range (commonly 8-12 ft for standard ceiling sensors). For open or irregular spaces, multiple sensors with overlapping coverage typically outperform a single high-range unit trying to cover the whole area.
What causes false triggers or missed detection in motion sensors?
False triggers commonly come from HVAC vents blowing across a PIR lens, sunlight or headlights sweeping the field of view, or microwave sensors picking up motion through walls from an adjacent space. Missed detection often results from mounting height outside the rated range, detection zones blocked by shelving or equipment, or PIR sensors facing a direction where a person walks directly toward the sensor rather than across its field of view (PIR is more sensitive to lateral motion).
Can motion sensors be used for safety interlocking on machinery?
Standard commercial PIR/microwave occupancy sensors are not safety-rated devices and should not be used as the primary safeguard for personnel protection near hazardous machine motion — that role requires safety-rated presence-sensing devices (light curtains, safety laser scanners) meeting the relevant machine safety standard. General motion sensors are appropriate for supplementary automation signaling, not as the sole safety function.
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