Why Mounting Matters
The performance of a PIR sensor depends heavily on its mounting height, angle, and location. Incorrect placement can lead to blind spots, false triggers, or missed detections.
Recommended Mounting Height
Most PIR sensors are designed for indoor use at heights between 1.5 and 2.5 meters (5-8 feet).
- 1.8-2.0 m (6-6.5 ft) is the sweet spot for general room coverage.
- Lower (1.5 m): Better for detecting pets or small children, but may miss tall adults.
- Higher (2.5 m): Wider coverage but may create blind spots directly below the sensor.
Coverage Pattern
The Fresnel lens creates a specific detection pattern. Typically, a PIR sensor covers a 90-120° horizontal angle and extends outward in a fan shape. At the specified height, the pattern covers an area roughly 5-10 meters in front.
Placement Do’s and Don’ts
Do:
- Mount in a corner for maximum coverage of a room.
- Aim the sensor so that the detection pattern crosses likely paths of movement.
- Keep the sensor away from heat sources (radiators, vents, windows with direct sun).
- Ensure the sensor’s view is not obstructed by furniture or plants.
Don’t:
- Mount behind glass or plastic covers that block IR.
- Point directly at a window (temperature changes outside can cause false triggers).
- Place near air conditioning vents (airflow can mimic motion).
- Install where the sensor might be exposed to rapid temperature changes.
Outdoor Mounting Considerations
Outdoor PIR sensors require weatherproof housings and careful placement:
- Avoid pointing at areas with moving vegetation (trees, bushes).
- Consider using pet-immune lenses to avoid animal triggers.
- Mount under eaves to protect from rain and direct sun.
- Be aware of temperature extremes; some sensors have limited operating range.
Adjusting Detection Direction
Many PIR sensors have a swivel bracket allowing you to tilt and pan the sensor. After mounting, test the coverage by walking through the area and marking where detection occurs. Adjust as needed.
Dealing with Blind Spots
No single PIR sensor covers 100% of an area. To eliminate blind spots:
- Use multiple sensors with overlapping coverage.
- Combine with other sensor types (microwave, ultrasonic) for dual-tech motion detectors.
- Consider sensors with specialized lens patterns for specific coverage needs.
Testing Your Installation
After mounting, perform a “walk test”:
- Connect an LED or buzzer to the sensor output.
- Walk slowly across the coverage area at different distances.
- Note where detection is reliable and where it fails.
- Adjust the sensitivity or reposition if necessary.
Conclusion
Proper mounting is essential for reliable PIR operation. Follow these guidelines to maximize detection performance and minimize false alarms.