Introduction
If your property is near a road with buses or a railway line, passing large vehicles may trigger your PIR sensors. These vehicles are large, warm, and moving – perfect targets for a PIR sensor.
Why It Happens
Buses and trains have large, warm engines and exhaust systems. Even at a distance, they can emit enough IR to be detected, especially if the sensor has a clear line of sight.
Symptoms
- False triggers at regular intervals corresponding to vehicle schedules.
- Triggers occur even when no one is on your property.
Solutions
1. Reposition Sensor
Aim the sensor away from the road or railway. Use walls, fences, or vegetation to block the line of sight.
2. Use a Narrower Lens
Replace the lens with a curtain (long-range) type that has a narrow horizontal field, reducing the chance of seeing passing vehicles.
3. Reduce Sensitivity
Lower sensitivity may prevent detection of distant vehicles while still detecting closer intruders.
4. Use a Mask
Create a custom mask for the lens that blocks the specific direction of the road. Masking tape can be used experimentally.
5. Use Dual-Tech Sensor
Dual-tech (PIR+microwave) sensors require both technologies to trigger. Vehicles may trigger PIR but not microwave (or vice versa), reducing false alarms.
6. Time-Based Filtering
If vehicle schedules are predictable, you can ignore triggers during known vehicle times – but this is risky.
Case Study: House Near Bus Route
A homeowner’s PIR security light triggered every time a bus passed. Adding a fence that blocked the line of sight to the road solved the problem.
Conclusion
Large vehicles can be a challenge, but physical barriers and lens changes are effective solutions.