Need Perimeter Intrusion Detection? Here Are Your Options and How to Decide

With IFSEC Global recently reporting how the rising number of intrusions is fuelling robust growth in the perimeter security market its worth revisiting this specialist intruder detection subject.

There are a number of detection technologies in today’s arsenal today for detecting persons or vehicles penetrating a facilities perimeter boundary. However, no single optimum solution for all security applications exists, and each technology type has its place dependent on the site and organisation requiring protection.

Five major factors influence the choice of technology when considering implementing a perimeter detection system; risk, location, terrain, structure and standards.

Foremost, the technology must be commensurate with the risk requiring protection and the sophistication of any potential assailant(s) and their likely method of penetration. The chosen technology must be suitable for the geographic location; harsh environment, climate; rainy, dry etcetera and the terrain and topography; hilly, marsh, flat.

It also needs to be appropriate for the structure in will be installed on or within. Finally, it must meet with any national or local standards – eg  BS EN5013 – or planning permission.

Dependent on the organisation or risk it is also advisable to consider using complementary technologies to either increase detection rate (security) or decrease nuisance and false alarm rates by requiring both technologies to go into alarm before triggering an alert.

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Good housekeeping

Of equal importance with perimeter detection technology is good house-keeping. Keeping structures in good repair is essential. Maintaining the grounds, cutting down bushes and clearing litter adjacent to and around sensors is necessary.

Although this list is not exhaustive, it does provide examples of influencing factors.

Where high level but discrete security is required – such as a high net worth individual or national monument – or where no perimeter physical barrier exists and there is open area, the use of a buried wire system would prove appropriate.

However, what needs detecting – human or vehicle – the method of attack, the geographic location and the ground composition need consideration, ensuring the correct type of buried wire system is specified.

Investigating planning consents may also be necessary. Such a system is difficult to defeat, provides a wide detection zone and is immune to most environmental nuisance alarms.

Where there is an existing suitable perimeter fence, a fence-mounted continuous sensor cable can be attached directly to the fence, usually with UV-resistant cable ties. The sensor type either detects vibrations and uses sophisticated digital processing to ascertain if someone is climbing, cutting or lifting the fence or makes use of micro-phonic cable.

Alternatively, if there is no existing barrier but some form of physical barrier is required then a taut wire system would be appropriate. As the name suggests, multiple, horizontal, smooth or barbed wires tightly stretch along a typical segment of 60 metres that is connected to a sensor post located halfway between adjacent anchor posts.

An electro-mechanical sensor detects a predetermined amount of deflection in the cable to initiate an alarm. Clearly, topography needs to be considered and ground composition in the use of this technology to prevent burrowing or crawling under the fence.

Again, planning consent will almost certainly be required, as will good housekeeping, keeping the fence maintained and clearing litter and debris. Some of these fence-based systems are also applicable to perimeter walls.

Another solution, and one that is both cost -effective and suitable for protecting fence and walls, is fibre optic cable. These systems cover large distances and are moisture- and electo-interference-resistant.

Infrared sensors

For medium applications, the use of active infrared sensors (beams) or bistatic microwave systems, which tend to be cheaper than buried wire or fence-based solutions, should be considered. However, these systems require line of sight and can be prone to inclement weather or objects blowing.

For low risk use, external passive infrared detectors or microwave sensors, which are best suited to external areas of trap protection or to supplementing other detection methods, can prove a cost effective solution for low-level, unsophisticated challenges. However, though they are cheap and easy to install, they are also prone to nuisance alarms and relatively easy to nullify.

One of the most effective perimeter detection systems is the electric fence, which provides both a convincing deterrent and an alert should an attempt made to breach it. The main concern here is the accidental risk of electric shock to innocent people, making its use best restricted to protect access across or through a six inch high wall or behind a first-stage physical barrier.

Just as increasingly popular in securing perimeters is the use of thermal cameras. These devices are immune to weather effects and cover long distances and can incorporate either analytics or supplement other devices.

In conclusion, it is necessary to carefully evaluate the threat, the structure, terrain and location and carefully study the manufacturers’ literature to ascertain the most appropriate solution or combination of technologies for a given application and budget.

Reference material

a&s International ( August 2011) Sharpen Your Senses: Securing Boundaries with Perimeter and Intrusion Detection Technologies. [online] Available at  http://www.asmag.com/showpost/12041.aspx [Accessed on 27th October 2014]

BICSI (July 2012). Electronic Safety and Security Design Reference Manual, Third edition. BICSIÒ ISBN 1-928886-60-4