Fence-Mounted Vibration Sensors: Technology Guide

Fence-mounted sensors are the most widely deployed category of perimeter intrusion detection technology. They convert mechanical disturbances — climbing, cutting, lifting, or impact on a fence — into electrical signals that are processed to distinguish intrusion events from environmental noise.

This guide covers the principal sensor types, their operating principles, installation considerations, and the applications where each performs best.

How Fence Detection Works

Every fence-mounted detection system follows the same basic signal chain. A sensor attached to the fence fabric converts mechanical vibration into an electrical signal. A processor analyses the signal to determine whether it matches an intrusion signature or an environmental event. If the signature exceeds a threshold, the system generates an alarm and identifies the zone.

The critical differentiator between products is not the sensor itself but the signal processing. Modern systems use adaptive algorithms — and increasingly machine learning — to distinguish the short, high-energy signature of wire cutting from the sustained, low-frequency pattern of wind, or the periodic impact of rain.

Sensor Types

Microphonic Cable

A coaxial sensor cable runs along the fence, typically at or near the top. Disturbances to the fence create pressure waves that propagate through the cable, generating a voltage signal. An analyser at the cable's termination point processes the signal.

Microphonic cables offer continuous detection along their length with zone localisation typically at 3–5 metre resolution. Senstar's FlexZone is the most widely deployed microphonic system globally, installed on hundreds of thousands of metres of fence across correctional, military, and utility sites. The cable itself is passive, making it suitable for hazardous environments.

Strengths: Continuous coverage, zone localisation, proven reliability, works on most fence types.

Limitations: Sensitivity varies with cable routing. Sharp bends attenuate signals. Performance depends on fence tension and condition — loose fabric generates excessive mechanical noise.

Piezoelectric and Accelerometer Sensors

Discrete sensors are mounted at regular intervals along the fence, each covering a defined zone length (typically 50–100 metres). Each sensor contains a piezoelectric element or MEMS accelerometer that converts vibration into an electrical signal.

Southwest Microwave's MicroPoint system uses discrete accelerometer sensors mounted every 3 metres with zone processors covering up to 300 metres. RBtec's RaySense mounts piezoelectric sensors that communicate wirelessly, eliminating the need for cable runs between sensor points.

Strengths: Individual sensor failure does not compromise the entire zone. Easier to retrofit on existing fences. Some systems support wireless communication, reducing installation cabling.

Limitations: Detection gaps can occur between sensors if spacing is too wide. Discrete mounting points can be identified and avoided by an informed adversary.

Strain and Tension Sensors

These systems detect changes in mechanical tension on fence wires or panels. A force is applied to the fence — climbing loads the top rail, cutting releases tension in individual wires. The sensors measure this change against a calibrated baseline.

Gallagher's Tension Sensor System monitors individual wires on high-security mesh fences, detecting cut, climb, and spread attempts based on changes in tension. CIAS Elettronica's SIOUX PRO2 uses micro-mechanical sensors that respond to the deformation pattern of the fence panel.

Strengths: Very low false alarm rates because the system responds to sustained mechanical loading rather than transient vibration. Excellent for high-security applications where nuisance alarms are operationally costly.

Limitations: Requires well-maintained, properly tensioned fences. Not suitable for chain-link or other flexible fence types that have high inherent movement.

Fence Compatibility

Not every sensor works on every fence type. This is the most common source of performance problems in the field.

Chain-link: Microphonic cable and piezoelectric sensors perform well. Tension sensors are not suitable due to the inherent flexibility of chain-link mesh. Signal processing must account for higher ambient movement than rigid fence types.

Welded mesh (358 and similar): All sensor types perform well. The rigid construction provides a clean vibration transmission path and low ambient movement. This is the easiest fence type to protect with any PIDS sensor.

Palisade: Discrete sensors mounted on individual pales work effectively. Microphonic cable can be run along the top rail. The open construction means wind loading varies significantly with pale spacing and height.

Concrete walls and masonry: Accelerometer sensors bonded to the surface detect cutting, drilling, or impact. Microphonic cable is not applicable. Sensitivity must be set carefully because concrete transmits vibration over long distances, making localisation difficult.

Timber fences: Poor vibration transmission limits the effectiveness of most sensor types. Timber absorbs rather than transmits mechanical energy. Accelerometer sensors at close spacing can work but are rarely cost-effective.

Installation Factors

Fence condition is the single most important factor in fence sensor performance. A fence with loose fixings, broken ties, or sagging fabric will generate continuous mechanical noise that overwhelms most signal processing systems. Any fence sensor installation should begin with a fence survey and remediation of defects.

Zone length affects both sensitivity and operational response. Longer zones (200–300 metres) reduce hardware costs but create larger search areas for responding guards. Shorter zones (50–100 metres) improve localisation but increase the number of processors, cabling, and commissioning effort.

Environmental exposure drives algorithm tuning. Sites exposed to sustained high winds, heavy rainfall, or proximity to road and rail traffic require more aggressive noise filtering, which can reduce sensitivity to low-energy intrusion events. Sheltered sites in temperate climates are the most straightforward to commission.

Wildlife is a persistent nuisance alarm source. Animals climbing, rubbing against, or pushing through fences generate vibration patterns that can resemble intrusion events. Some systems offer specific wildlife rejection algorithms. Others rely on integration with camera verification to confirm or dismiss fence alarms.

Integration with Other Systems

Fence sensors rarely operate in isolation. A typical installation integrates fence detection with CCTV for alarm verification, access control for gate monitoring, and a security management platform for alarm handling and reporting.

The most effective integration pattern is automatic camera slew-to-alarm: when a fence sensor triggers, the nearest PTZ camera or fixed camera automatically displays the alarm zone on the operator's monitor. This reduces verification time from minutes to seconds and dramatically improves response effectiveness.

Modern fence sensor systems provide alarm outputs via dry contact relays, serial protocols (RS-485), or IP-based interfaces. Increasingly, vendors offer native integration with major Video Management Systems (VMS) — Milestone, Genetec, and Lenel being the most common — enabling unified alarm management across the entire security system.

Key Vendors

Southwest Microwave — MicroPoint II cable-based system, INTREPID MicroTrack buried system. US-based, strong in government and military markets.

Senstar — FlexZone microphonic cable, OmniTrax buried sensor, LM100 laser mesh. Canadian, broadest PIDS product portfolio in the market. Acquired Blickfeld (LiDAR) in late 2025.

Gallagher — Z10 Tension Sensor System, integrated with Gallagher Command Centre access control platform. New Zealand-based, strong in commercial and correctional markets.

RBtec — RaySense accelerometer sensors with wireless communication, Iridum taut-wire system. Israeli, established in military and border applications.

CIAS Elettronica — SIOUX PRO2 micro-mechanical fence sensor, MARTE microwave barriers. Italian, strong in Southern European and Middle Eastern markets.

When to Choose Fence Sensors

Fence-mounted detection is the right choice when the facility has a defined fence line in reasonable condition, when budget constrains the use of more expensive volumetric technologies, and when the operational team can respond to zone-level alarm localisation.

Fence sensors are not the best choice for very long perimeters (above 5 km) where the cost of cabling and zone processors accumulates rapidly, for sites without a physical fence, or for applications requiring precise target tracking and classification beyond simple intrusion detection.