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SecurityWorld Online Magazine

CCTV Surveillance

Access Control

Biometric ID

Alarm & Detection

Security Parts & Devices

Integration & Convergence

Alarm & Detection

Perimeter Security: The First Line of Defence

Perimeter protection is becoming a growth area for astute end-users in the security industry. The subject is a hot topic at trade fairs and the marketplace is keen to debate what this sector is about. Chris Norton, UK Managing Director of Senstar-Stellar, considers developments.

By Chris Norton



Recent advances in CCTV monitoring and scene analysis, particularly the advent of IP-addressable cameras, has obscured a fundamental truth.  A CCTV image of an intruder is nearly always after the fact; it is rarely a preventative tool but nearly always an observational one.

By contrast, perimeter protection is often a deterrent if the device is overt and even if it is covert, the technology always forms the first line of defence. 




In recent site evaluations for end-users, Senstar-Stellar has found that the primary feature demanded of intruder detection systems is minimizing unnecessary alarms.  This is one of many areas in which Senstar-Stellar has consistently outperformed its competitors and built a platform that has placed it at the forefront of the perimeter protection market.

Clients expect a delicate balance between minimal ‘vulnerability to defeat’ and zero or negligible alarms not arising from security threats.  They are asking perimeter protection vendors for sophisticated links to their CCTV systems so that sensors -- both visible and covert -- form a reliable trigger for cameras and the recording of live situations.  Buried sensors are proving increasingly popular since their covert nature not only makes them difficult for an intruder to avoid but they cannot be targeted by vandals.  They have the added advantage of leaving the visual aesthetics of a site intact.

Increasingly, customers are demanding ‘double knock’ protection whereby the first trigger is an outlying one -- usually a volumetric sensor in the form of buried cable -- followed by verification of an intrusion on the building perimeter through fence or wall-mounted sensors.  Senstar-Stellar can provide both forms of protection and ensure they combine effectively.  Demands for ‘double knock’ protection do not come solely from end-users and such requirements are increasingly common in documents from the International Standards Organisation (ISO) and the criteria of similar authorities worldwide.

It is common for suppliers of perimeter protection systems and their clients to establish a ‘trade off’ weight range.  Anything below the range is considered to be a ‘nuisance’ alarm such as a small mammal, while anything above the range even at the lower limits is treated as a potential intruder -- perhaps a man crawling on all fours and so spreading his weight.

Body mass is not the only factor used and targets can be assessed according to their electrical conductivity, dimensions and pattern of movement.  ‘Nuisance’ alarms such as wildlife should be distinguished from ‘false’ alarms that come from an unidentified source.  Both can erode user confidence in a system and prove expensive.  Leading providers of intrusion protection invest heavily in R&D to ensure their systems keep unwanted alarms to a minimum, filtering out potential triggering from the elements and wind-blown debris as well as animals.  Senstar-Stellar’s detection systems minimize nuisance and false alarms, so making the equipment cost-effective and allowing it to be a backbone of site security.




How alarm criteria are set and combined will often depend on whether the site is manned or not, and whether it is adjacent to or remote from police and emergency services.  Advances in perimeter intrusion systems and the advent of surveillance cameras that can be viewed over the Internet are allowing facility managers to monitor remote, inhospitable sites where manned guarding is impractical both logistically and in terms of cost.  Simple installation methods, particularly cable plough techniques, mean that buried sensors have become increasingly easy to implement.  The cable plouw technique has vastly reduced installation costs and brought the buried sensor approach within the budget of most projects.

High quality covert sensors can be fine-tuned according to the nature of the electromagnetic field created around buried cables.  When an intruder disturbs the field, his location is calculated to the nearest meter and an alarm is declared.  In the case of a networked application, the alarm is instantly communicated over the sensor cables to a PC-based central control system where the intruder’s coordinates are displayed on a map or schematic.

With cost of an ever-present factor, it should be noted that a premium buried cable system can not only provide detection but also distribute power and collect data.  The ability to distribute low voltage power on such cables can provide significant financial savings on other wiring requirements.  Such factors have huge implications for overall costs.

Senstar-Stellar is committed to open protocols and has ensured that its products integrate with the GUI ‘head end’ of all the major CCTV manufacturers since precise coordinates are of little use if the intruder cannot be viewed on a monitor. 

In turn, surveillance consultants and security operatives appreciate the intelligence inherent in leading perimeter detection systems since the amount of time spent watching eventless video is minimized and intruders can be seen instantly. 




Despite all the advantages of covert perimeter protection, the tangible nature of a fence can present an imposing appearance and act as a deterrent.  Conventional barriers may still be the best solution to a client’s expected threat, and may be better suited to a site’s conditions and environment than buried sensors.

Senstar-Stellar offers fence and wall-mounted sensors that are usually installed retrospectively on an existing structure. Again there can be cost-savings here.  Fence-mounted sensors prove economical on refurbishment projects in which best use must be made of original fabrics.  Despite the sophistication of volumetric detection, many sites are suited to simple techniques and the simplest approach will always be the methodology whereby an alarm is activated through vibration resulting from an attempt to cut or climb a fence.

Such an approach may be uninvolved but the methods are certainly not crude.  Signals on fence-mounted systems are analysed at a microphonic level or the perimeter can be scrutinized for optical disturbance.  Minute flexing as well as clumsier attempts to cut or climb a barrier are registered as alarms with a remarkably low vulnerability to defeat and high rejection of nuisance alarms.



The fence approach is often the optimum solution at large industrial premises where factors such as cost and speed of installation are key.  Palisade fences where the threat is usually climbing rather than cutting can often be protected effectively with sensors. Bare metal fabric rather than a vinyl coating is preferable but the latter can be alarmed effectively if the amount of sensor cable is doubled up.

Covert and barrier-mounted alarm systems can be used at any industrial site as well as prisons and nuclear power stations or other sensitive parts of the infrastructure.  Airports and military bases with their massive perimeters have obvious needs for protection which can be covert or overt.  In the current political climate the need to protect aviation sites cannot be overstated while border control to prevent the movement of terrorists is another significant application.

In the past 12 months Senstar-Stellar has supplied perimeter intrusion solutions to a London airport, to a major Far Eastern car manufacturer operating out of the United Kingdom, to one of the world’s largest mobile network providers and to a power station in England.


Chris Norton is UK Managing Director of Senstar-Stellar (



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