PIDS Technology Primer: A Guide to Detection Modalities

Perimeter Intrusion Detection Systems (PIDS) rely on a range of sensor technologies to detect, locate, and classify threats along a facility's boundary. Each modality offers distinct advantages in detection range, environmental resilience, false alarm management, and cost per metre of coverage.

This primer provides a practitioner-level overview of the principal detection modalities in current use, their operating principles, and the applications where each performs best.

Fence-Mounted Sensors

Operating principle: Electromechanical or piezoelectric sensors attached directly to fence fabric detect vibrations caused by climbing, cutting, or lifting. Signal processing algorithms distinguish intrusion signatures from environmental noise (wind, rain, wildlife).

Key vendors: Southwest Microwave (MicroPoint), Senstar (FlexZone), Gallagher (Z10 Tension Sensor), RBtec (RaySense), CIAS (SIOUX PRO2).

Best for: Chain-link, welded mesh, and palisade fences at commercial, industrial, and correctional facilities. Lower cost per metre than most alternatives. Detection accuracy depends on fence condition and installation quality.

Limitations: Performance degrades on poorly maintained or loosely tensioned fences. Environmental noise (high wind, heavy rain, nearby road traffic) can elevate nuisance alarm rates without careful tuning.

Buried Cable / Underground Sensors

Operating principle: Coaxial cables or fiber optic sensors buried in the ground detect pressure changes, seismic vibrations, or electromagnetic field disturbances caused by walking, running, or digging above the sensor line.

Key vendors: Senstar (OmniTrax), Southwest Microwave (INTREPID MicroTrack), SensoGuard.

Best for: Sites requiring covert detection with no visible sensor infrastructure — airports (runway exclusion zones), government facilities, military installations. Unaffected by visual obstruction.

Limitations: Installation requires trenching, making retrofit expensive. Soil conditions (rocky, saturated, frozen) affect performance. Subsurface utilities complicate routing.

Active Infrared Barriers

Operating principle: Paired transmitter–receiver columns project infrared beams across an open area. An intrusion is registered when one or more beams are interrupted. Multi-beam configurations reduce false alarms from animals or debris.

Key vendors: SORHEA (MAXIRIS, SOLARIS), OPTEX (AX series), Takex.

Best for: Wall-top protection, rooftop access points, and open areas between buildings where fence-mounted sensors are impractical. Clean detection zones with low nuisance alarm rates when properly aligned.

Limitations: Line-of-sight requirement limits use on uneven terrain. Fog, heavy snow, and direct sunlight can degrade performance on lower-end models. Coverage is linear — each beam pair protects a single line.

Microwave Barriers

Operating principle: A transmitter generates a microwave field between two points. Movement within the detection zone alters the field pattern, triggering an alarm. Bistatic (separate Tx/Rx) configurations are standard for perimeter applications.

Key vendors: Southwest Microwave (INTREPID MicroWave), CIAS (Murena), SORHEA.

Best for: Open perimeters, gate gaps, access roads, and areas requiring volumetric detection without physical barriers. Effective in rain, fog, and dust. Range typically 50–500 metres per link.

Limitations: Detection zone width varies with range — longer links produce wider zones, potentially triggering on activity outside the protected area. Vegetation growth into the detection zone causes nuisance alarms. Requires clear line of sight.

Fiber Optic Distributed Acoustic Sensing (DAS)

Operating principle: A laser interrogator sends pulses along a fiber optic cable. Acoustic vibrations along the cable (from climbing, cutting, walking, or vehicle movement) cause measurable changes in the backscattered light signal. Signal processing localises the disturbance to within metres along cables spanning tens of kilometres.

Key vendors: Sintela (Onyx), Fiber SenSys / OPTEX (EchoPoint), Gato Security (F7-DAS), Future Fibre Technologies (Aura Ai).

Best for: Very long perimeters — borders, pipelines, railways, large industrial sites. A single interrogator can monitor 40+ km of fiber. Uses standard telecommunications-grade cable, enabling use of existing buried fiber infrastructure.

Limitations: Sensitivity to environmental acoustics requires AI-based classification to manage nuisance alarms. Interrogator hardware cost is high (offset by low per-metre cable cost on long runs). Performance varies with cable type and installation method.

Radar

Operating principle: Ground-based radar emits radio frequency energy and analyses reflections from objects within the detection zone. Modern perimeter radars use FMCW (Frequency Modulated Continuous Wave) technology to detect, track, and classify moving targets across wide areas.

Key vendors: Navtech Radar (AdvanceGuard), Axis Communications (D2100 series), Blighter Surveillance Systems, Magos Systems.

Best for: Wide-area surveillance — airports, military installations, borders, marine approaches. Single sensors cover large areas (Navtech claims 79 km² per sensor at 5 km range). Operates in darkness, fog, rain, and dust.

Limitations: Classification accuracy is lower than camera-based systems — radar detects that something is moving, but determining what it is typically requires camera verification. Cost per sensor is high, though cost per square metre of coverage can be low for large sites.

LiDAR

Operating principle: Pulsed laser light creates high-density 3D point clouds of the detection zone. Software analyses the point cloud to detect, classify, and track objects based on size, shape, and movement. Privacy-compliant — no identifiable imagery.

Key vendors: Ouster (Gemini), Blickfeld (QbProtect), OPTEX (REDSCAN Pro).

Best for: Sites requiring precise volumetric detection with low false alarm rates — data centres, substations, rooftops, and confined perimeters. 3D classification distinguishes people from animals and debris. Works in complete darkness.

Limitations: Range is shorter than radar (typically 30–100 metres per sensor). Performance degrades in heavy rain, fog, and snow. Cost per sensor is currently higher than most alternatives, though pricing is falling as automotive LiDAR technology drives manufacturing scale.

Thermal Imaging

Operating principle: Uncooled microbolometer sensors detect infrared radiation emitted by people, animals, and vehicles. Thermal cameras produce imagery based on temperature differences, enabling detection in total darkness without illumination.

Key vendors: SightLogix (SightSensor), Axis Communications (Q-series thermal), FLIR/Teledyne, Hikvision (DeepinViewX), Bosch (DINION 7100i IR).

Best for: Long-range outdoor detection (200–1,000+ metres depending on lens), especially at sites where visible-light illumination is impractical or undesirable — military, border, and critical infrastructure perimeters. AI analytics on thermal video enable automated classification.

Limitations: Thermal cameras detect heat signatures, not identity — visual verification requires a paired visible-light or PTZ camera. Performance narrows in extreme heat (when ambient temperature approaches body temperature) and during solar loading of surfaces.

Choosing the Right Modality

No single technology covers all perimeter scenarios. Most high-security deployments use a layered approach combining two or more modalities — typically a primary detection layer (fence sensor, DAS, or radar) with a verification layer (thermal camera or LiDAR) and an integration platform to correlate alerts and manage response.

The right combination depends on perimeter length, terrain, environmental conditions, threat profile, budget, and the false alarm tolerance of the monitoring operation. Understanding the physics and practical constraints of each modality is the starting point for any informed PIDS specification.