Perimeter Intrusion Detection Systems

Barrier-mounted PIDS are installed on a physical barrier, such as a high-security fence, to enhance detection and delay capabilities. These systems work in conjunction with the barrier to detect unauthorised intrusions. The advantage of barrier-mounted PIDS is the physical delay that the fence or wall provides. In addition, some PIDS can protect an entire perimeter using a single continuous cable which reduces costs. On the downside, high winds can cause fence and topping vibrations, leading to false alarms, which must be accounted for in system design. Ultimately, the effectiveness of a barrier-mounted PIDS is influenced by the type of barrier used; a rigid design and long-lasting construction and materials are key.

Common types of barrier-mounted PIDS include microphonic cable systems which use piezoelectric cables attached to the fence fabric to detect vibrations caused by an intruder attempting to breach the barrier. These are highly discreet.

Geophones and Point Sensor Systems are another type of barrier-mounted PIDS. These consist of low-frequency microphones or accelerometers mounted on the fence structure to sense vibrations caused by intrusion attempts.

Electric Fence Systems are also classed as PIDS. Featuring multiple horizontal, non-lethal high-voltage wires, these systems trigger an alarm if the wires are cut or grounded, either by contact between wires or with the metallic support structure. If an existing fence serves as the host structure, its strength and foundation stability must be assessed. Electric fence attachments are the opposite of discreet, and serve a high deterrence factor. The downside of these systems is that the wire strands require regular inspection and build-up can occur on the insulators e.g. salt in coastal locations, which may produce false alarms. Humidity can also affect their performance.

Ground-based PIDS are buried beneath the surface and can be deployed with or without a fence to detect intrusions. These systems operate by sensing movement or pressure disturbances in the ground. Ported coaxial cable, also known as leaky feeder systems, use specialised cables to generate a radio frequency electromagnetic field that detects intruders by identifying changes in the field caused by movement. Microphonic cable systems rely on piezoelectric cables to sense vibrations created by an intruder walking across the protected zone. Another type, fluid-filled tube systems, consists of two tubes filled with fluid that register pressure changes in the ground when an intruder steps on or near them. Each of these systems provides a covert means of intrusion detection, making them suitable for various security applications.

Ground-based PIDS can be expensive for short perimeters due to the high cost of the processing unit, making them more cost-effective for larger installations. When not deployed alongside a physical barrier, a prompt response to alarms is crucial to ensure effective security. Additionally, these systems have high installation costs and can cause significant disruption during deployment. Environmental factors, such as surface water, can reduce their effectiveness, potentially leading to false alarms or decreased sensitivity. Furthermore, maintenance costs are higher compared to other systems, as fluid-filled tube variants require annual pressure checks to ensure optimal performance.

Free-standing PIDS are designed to monitor an area above ground and can be deployed with or without a fence. These systems use various detection technologies to identify intrusions. Active infrared systems consist of a transmitter and receiver module, detecting intruders when one or more infrared beams are disrupted. Monostatic or Doppler microwave systems identify movement by detecting the reflection of radio waves, while bistatic microwave systems sense intrusions by responding to disruptions in radio wave transmission. Additionally, passive infrared systems detect movement by recognizing the infrared heat signature emitted by the human body. These systems provide flexible and effective security solutions for open areas and perimeters. Weaknesses of these systems include susceptibility to the effects of fog, and they are also only designed to be installed over flat ground as undulations can create dead zones. They also have poor immunity to changing temperatures, so they are less suited for outdoor environments.

Rapidly deployable detection systems can utilise any of the above detection methods. These systems are designed for quick installation, allowing two people to set them up within a short timeframe. However, they should not remain in operation for more than two weeks without being recommissioned to ensure continued reliability and effectiveness.