Mechanical event vs path break
Fence detection — typically a vibration cable or fibre-optic sensor — detects mechanical disturbance of the fence fabric: climbing, cutting, lifting.
Beam detection — infrared or microwave — establishes a sensing path between two points and triggers when that path is interrupted.
Line vs zone
Fence sensors follow the fence line, no matter how it curves. Coverage is exactly the perimeter.
Beams provide straight-line coverage between two points. Multiple beams stack to create a zone curtain.
What sets each one off
Fence sensors are affected by wind, fence quality, animal contact and vegetation against the fence.
Beams are affected by wildlife crossing, vegetation growth into the beam path and (for IR) heavy weather. Microwave beams are more weather-tolerant.
Layered perimeter sensing
On high-security perimeters, fence sensors and beams are layered — fence detection at the boundary, beams just inside as a confirmation layer, often with CCTV verification overlaying both.
Fence detection vs beam detection
Different physics, different failure modes. Choose by site shape and threat profile.
| Feature | Fence detection | Beam detection |
|---|---|---|
| Sensor location | Mounted on fence | Free-standing transmitter / receiver |
| Coverage shape | Follows fence line | Straight line / stacked curtain |
| Detects climbing & cutting | Yes | Indirectly (when crossed) |
| Detects open-ground crossing | No | Yes |
| Wind sensitivity | Higher | Low |
| Wildlife sensitivity | Moderate | Higher for IR |
| Best for | Existing fenced perimeters | Open ground, gaps in fencing, courtyards |
| Pairs well with | Perimeter CCTV, PIDS analytics | Fence sensors, CCTV verification |
Which perimeter sensor should you specify?
Fence detection is the default where a continuous fence already exists. Beam detection is the strong choice for open ground, courtyards, gate-line confirmation and as a layered confirmation sensor.
- Existing continuous fence line
- Climbing or cutting is the primary threat
- Long, regular perimeter
- Open ground, no fence
- Courtyards or gaps in the fence line
- Confirmation layer behind fence detection
Frequently asked questions
Can I use beams without fence sensors?
Yes — beams are widely used on their own, especially across courtyards, between buildings and on open boundaries.
Are microwave beams better than infrared?
Microwave beams are more weather-tolerant and have wider detection volume. IR is cheaper and sharper but more sensitive to wildlife and fog.
Can I use both on the same perimeter?
Yes — combining fence-mounted detection along the main perimeter run with beam detection across gates and short critical sections is a common high-security design pattern. The two technologies detect different threat vectors, and combining them gives layered detection that is significantly harder to defeat than either alone. Integration through a common VMS makes the combined operation manageable.
How is fence detection affected by fence condition?
Fence-mounted detection assumes the fence itself is in serviceable condition — taut, well-fixed and free of loose panels. A poorly maintained fence generates false alarms and undermines detection reliability. A fence survey and any required remediation should be scoped as part of any fence-mounted PIDS project rather than assumed as free existing infrastructure.
What weather conditions cause beam detection failures?
Fog, driving rain and heavy snow can attenuate beam signals to the point of triggering fault or false-alarm events. Modern dual-tech beams — combining microwave and active infrared — are much more resilient than single-technology beams. On sites where fog is common, dual-tech should be specified from the outset rather than added as a retrofit later.
Which has lower false alarms in a wildlife-rich environment?
Beam detection, generally — small mammals below the beam line pass under detection height, whereas fence-mounted sensors are triggered by animal contact with the fence itself. On rural or wildlife-adjacent sites, beam detection often outperforms fence-mounted alternatives on false-alarm rate, though fence detection remains preferred for its long-run coverage economics on longer perimeter runs.
How is zoning handled between the two technologies?
Both technologies support addressable zoning, but at different granularities. Fence-mounted sensors typically address in fifty to one hundred metre zones; beam systems are inherently zoned by transmitter-receiver pair. Alignment of zoning between technologies is a design consideration during specification and should follow the operational response model rather than each technology's native default zone size.
Talk through this comparison with a specialist
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