How to prevent detection overspill with VXI and VXS sensors
One of the most common challenges when installing outdoor PIR sensors is detection overspill: when the sensor detects movement outside the intended protected area. This can result in unwanted activations caused by pedestrians, vehicles, neighbouring properties, vegetation, or reflective surfaces.
Both the OPTEX VX Infinity (VXI series) and VX Shield (VXS series) sensors include several features designed to help installers create precise detection zones and minimise nuisance alarms:
1. Use lens masking to shape the detection area
The most effective way to eliminate overspill is by using the dedicated OPTEX masking seals supplied with the sensor. Different masking templates allow installers to remove specific PIR zones from the detection pattern.
Segment masking can be used to exclude specific disturbances.
Masking Seal 1
This template is made up of 14 smaller masking seals. These are used for individually masking out areas, such as a swaying tree in full foliage in the detection area.
Masking Seal 2
This area masking seal masks out the centre of the detection area, leaving an L-shaped area when pointing to the right, and a reverse L-shape when pointing to the left up to 12m range. This template is perfect for masking out areas that are commonly used, or have large numbers of people passing through them. They are also perfect for protecting access to potentially hazardous areas, such as a swimming pool, without being affected by the light reflection on the water.
Rectangular masking is ideal for preventing detection of adjacent roads, pathways, or public areas.
Masking Seal 3
This masking template creates a rectangular detection zone, up to 10m by 5m. This type of masking is useful to protect a parking area or yard and avoid overspill onto a public road for instance.
Masking Seal 4
This masking template produces a detection zone 1.5m deep. Common scenarios: town houses, or city homes where doors open straight onto paths.
Masking Seal 5
Choose this template if you wish to create a detection area of 10m by 5m This could be used to protect a patio, yard, parking area.
Masking Seal 6
Exactly the same concept as template 5, but this decreases the width of the zone to 1.5m, ideal to protect a narrower path and removing the possibility of overspill.
Because masking physically removes unwanted detection zones, it provides a reliable solution for challenging environments. Always use genuine OPTEX masking seals, as non-approved materials may interfere with the sensor's anti-masking functionality.
2. Select the appropriate detection range
Overspill is often caused simply by using a detection range that is larger than required. The VXI and VXS sensors offer five selectable detection ranges: 2.5m, 3.5m, 6m, 8.5m and 12m
As best practice, select the shortest range that still provides complete coverage of the protected area. Reducing the range can significantly improve detection accuracy and reduce unwanted activations.
4. Ensure correct mounting
Proper installation geometry plays a critical role in achieving accurate detection.
For optimal performance:
• Mount the sensor between 0.8m and 1.2m above ground level.
• Ensure the sensor is level and not tilted.
• Align the sensor parallel to the protected area wherever possible.
Even small alignment errors can cause detection zones to extend beyond the intended coverage area and lead to overspill.
5. Combine range, alignment and masking
In many installations, overspill is best addressed through a combination of adjustments rather than a single change. A recommended setup process is:
1. Set the required detection range.
2. Adjust the pyro alignment.
3. Apply masking where needed.
4. Fine-tune the sensor position and angle.
This structured approach helps create the cleanest and most accurate detection pattern.
6. Verify performance with a walk test
A walk test should always be completed before finalising the installation. Confirm that:
• Movement inside the protected area is detected consistently.
• Movement in excluded areas does not trigger the sensor.
Real-world testing remains one of the most effective ways to identify and eliminate overspill issues before the system is handed over.
7. Watch for common sources of overspill
Particular attention should be given to areas containing:
• Roads and driveways
• Pedestrian walkways
• Water surfaces and reflections
• Moving vegetation
• Neighbouring properties
If these areas fall within the detection pattern, consider applying masking or adjusting the sensor geometry to maintain accurate coverage.
Installer Tip
If overspill persists after installation, avoid relying solely on sensitivity adjustments. In most cases, the issue can be resolved more effectively by revisiting the sensor geometry, specifically the combination of detection range, alignment, and masking.
By following these steps, you can maximise the performance of VXI and VXS sensors while ensuring reliable detection only where it is needed.
