Can Shadows Trigger A Dual Tech?

Can Shadows Trigger A Dual Technology Sensor And What’s The Solution?

Can Shadows Trigger A Dual Tech – In our experience it’s not shadows but sudden increases in light that trigger a dual technology sensor – even a very high-end dual tech is not immune to being nudged into alarm by these changes. This is especially the case if the light change or strong light source is accompanied by movement in the scene that also triggers the microwave.

Even though most quality PIR sensors have resistance to trigger by white light, all PIR sensors and dual tech sensors are inherently vulnerable to increases in light. In our experience this is especially the case if the changes occur across the entire detection angle – such as when a thick cumulous cloud covers and then uncovers the sun on an otherwise sunny day with light levels of 100,000-130,000 lux.

In the short video above a light change is accompanied by a car top left but there are complications to what’s happening in this scene. The sensor’s sensitivity settings are at the highest level – it will detect almost any movement across its detection fields. This might arguably include movement detected only by the microwave at long range – this car is 35-40 metres from the sensor. Further, the intrusion of the car top left may impact on the rendering of still images captured – but that’s not certain.

It’s tempting to say just buy a sensor with white light immunity. However, this immunity is most effective against headlights and strong torch beams – global light changes are still a false alarm threat. The issue with light is that it triggers an electrical signal from the pyroelectric sensor of a PIR – if this voltage is within a particular range, it may be interpreted as an alarm event.

In this image a light change and a car top left triggered a single alarm event.

Sensor technologies you’re looking for to resist light changes include optical filtering and signal processing in which algorithms analyse the frequency and pattern of detected signals, ignoring those inconsistent with thermal profiles of human movement.

Dual pyroelectric elements can be configured to detect slightly different heat patterns consistent with human thermal signatures, but they work best against artificial light sources. Dropping pulse count may help, but in our experience, this works best against localised triggers like birds, rather than global light changes.

Your best option might be to change the sensor direction so more of the scene is shaded during the day in order to reduce the impact of light changes. You might also install a PIR camera sensor to deliver alarm verification but it won’t stop alarm events occuring.

A monitoring station can make a decision about an alarm event based on the alarm trigger patterns. Light triggers typically occur occasionally on a single zone – often at the same time of day in a given season. We get them on a front balcony in the morning between 10-12, especially if there are gusty winds. Comparatively, an intruder will cause a cascade of triggers across multiple zones, generally at night.

You can discover a light-resistant dual technology sensor here or read more SEN news here.  

“Can Shadows Trigger A Dual Technology Sensor And What’s The Solution?”