An effective perimeter security system must include a combination of several mutually supporting physical barriers, electronic detection systems and manual procedures.

Where a physical barrier may deter a potential intruder and slow any attempted penetration of a perimeter it cannot typically alert a response team. Therefore other than random patrols, an effective response can be difficult to formulate.

The same principle applies to an electronic detection system which on its own has a visible deterrent value. Whilst it can detect an intruder attempting to penetrate a perimeter and alert a response team; without an appropriate physical barrier to slow the intruder the response team would be unable to react quickly enough to prevent the security breach or detain the intruder despite receiving an early alarm indication.

Security Layers

Perimeter systems comprise of a series of security layers using physical barriers, electronic systems and manual procedures. With all of these working together, they provide a system of defence in depth that is the essential basis of any successful security infrastructure:

1. Deter
2. Detect
3. Delay
4. React
5. Detain
6. Record

Deter
A primary factor when considering the implementation of any security system is to determine the profile the client wishes to present to the outside world.

For example a three-metre fence with coils of razor wire is unlikely to be deemed suitable for the front entrance of a shopping centre, while the same would be extremely desirable for a maximum-security prison.

The deterrent factor plays a significant role in the effectiveness of any security system where a risk of casual or impulse attack exists.
If a target looks secure and difficult to penetrate, most would be intruders would move on to a perceived easier target.

Security Fence and CCTV Camera.

Detect
If an intruder is undeterred in the knowledge that a target is protected by a security system; it becomes imperative that electronic sensors be deployed to detect and verify any breach of the physical security barriers being used.

The success value of an electronic sensor is measured in terms of Probability of Detection (i.e. 99.9/100 intrusion attempts detected) weighed against nuisance or false alarm rate (i.e. one un-attributed alarm per zone, per week); and of course both of these factors are weighed against the installed cost of the system.

Video Motion Detection.
Lighter patches show sensitised
zones on video display. Movement
in any of these zones will cause an alarm.

Fibre Optic Sensor.
Microbending of a fibre optic cable
attached to a fence causes an alarm
impulse to be passed to the fence electronics.
1 = light signal normal.
2 = light signal in alarm.

Fence Mounted Acoustic Sensor Cable. Chart showing
sensor cable signal uniformity - no alarms. A spike would
appear to indicate an alarm impulse (fence cut or climb).

Delay
Physical barriers are typically designed to delay an intruder. A single fence can take a few seconds to defeat; multiple fences will typically take longer. Higher fences will typically further increase the time it takes an intruder to gain entry to a site.

Every second of delay increases an intruder's chance of detection and detainment. Once detected, additional delay allows a response force time to apprehend the intruder.

If layers of physical barriers force an intruder to bring tools such as cutting tools, ladders, bridging tools, ropes etc to effect a breach in the perimeter, then the systems in place will have largely achieved their purpose.

Barbed and Razor Wire Fences.

React
Physical barriers will typically slow an intruder, whilst an electronic system will typically detect and report them. However this only has the desired result if there is a viable response team that can arrive at the scene of the event in a fast and efficient manner.

A staffed control room may be able to remotely track an intruder with a CCTV system; however suitable radio communications are typically recommended to enable a patrol or response team to zero in on the perpetrator.

CCTV, Radio and Receiver.

Detain
Members of a security patrol must have the correct tools to effectively gain control of any given situation to enable them to detain intruders.

Subject to the application, vehicles may be utilised, typically a uniform and almost always some level of executive authority within the framework of the organisation they are working for.

Training of security personnel is extremely important; and the level to which they are trained is governed primarily by internal security policy, and based upon what the guard force is being employed to protect.

A range of options should be considered when formulating a response plan which can include, but not be limited to tools of force ranging from batons, wrist restraints and body armour to tazers, pepper sprays and firearms. Selected equipment should always conform with local legislation, whilst providing the guardforce with the ability to confidently maintain control in an orderly and efficient manner whenever possible.

Weapons used to detain.

Record
In recent times, recording, accountability and verification of events and incidents is proving more important than ever before. We can find no reason to expect that this growing importance will diminish in the foreseeable future.

Previously, recording of incidents was limited to an entry in a log book. Today, the same type of information is more often viewed on video and recorded digitally or to magnetic storage medium. These records typically require the same protection as the information or material the security system was put in place to protect.

This almost always means use of password protection for management functions in security software, Logging on and off by console operators, and physically securing redundant storage systems to prevent unauthorised manipulation of data. Data that could eventually be utilised as evidence.

Console, Digital Video Recorders (DVR) and CCTV Screens.

Standard Operational Procedures

Even the most formidable physical barriers and electronic systems can be ineffective if strong Security Policy and Standard Operational Procedures (SOP) are not in place.

Whilst basic policy and SOPs are drafted during the initial threat assessment and risk analysis phase, these are both dynamic documents which develop and grow to take into account local, social, economic, environmental and political changes; at the same time they must suit the various security systems selected and utilised.

Policy papers and SOPs, are an essential part of any long term security plan as is a Concept Document which names specific types (genus, not brand names) of physical barriers, electronic systems and procedures in general terms.

Consideration and expansion of these three document streams enable the smooth establishment and implementation of a cohesive integrated security solution within the target facility. At the same time the process establishes the basis for an auditable trail, which will bring out the engineering logic behind the selection of any particular aspect of the final security solution selected.

Selection of the appropriate electronic systems is one of the more critical aspects of system selection. Prevailing environmental conditions directly affect the performance of outdoor electronic systems more than other components.

Layers of mutually supporting electronic
and physical security systems, thougthfully
applied, will deter, delay and ultimately
detect even the most determined intruder.

Poor product selection can result in nuisance or false alarms, which can gravely reduce the integrity of the system. If nuisance alarms are allowed to continue the operator confidence can quickly become seriously eroded, and the entire system integrity will be at risk.

The product and procedures selected should be validated by an auditable document trail, which clearly and succinctly establishes their suitability for the job.
Product suitability can be determined by choices based on sound engineering practice and security design experience.

Closed Circuit Television (CCTV)

A perimeter system will typically contain Closed Circuit Television (CCTV) designed to provide a view of most, if not all parts of the perimeter and other key areas within a facility, these systems should be flexible enough to provide a view of more than one area of the fence line being approached.

CCTV should comprise good quality Charged Coupled Device (CCD) cameras able to produce pictures suited for the environment in which they are to operate.

The switcher controlling the cameras should be able to provide pictures instantaneously from the zone(s) in alarm and allow unrestricted viewing to any pan, tilt and zoom (PTZ) cameras attached to the system.

Lens sizes should be carefully selected to provide useable images from any part of the site. PTZ lenses must be able to cope with the magnification process involved when zooming in on smaller objects in the vicinity of the perimeter.

Digital Video Recorders (DVR) are an important component of the perimeter surveillance as they allow an operator to immediately review the events leading up to an incident and a full display of the entire event.

DVR's continuously record all cameras and provide networking between banks of cameras thus enabling some redundancy within a system.

There are definite benefits for the selection of DVR's over the use of analogue VCR's and magnetic tape video cassettes. Digital images retrieved from DVR's do not deteriorate when copied and so may be used as evidence and training much more readily.

Video Motion Detection (VMD)

While CCTV Cameras can provide a view of the perimeter, the use of Video Motion Detection (VMD) on these same cameras has the advantage of providing surveillance and detection within the same structure.

VMD Systems look for movement in the pre-determined detection areas and should the subject be of the target size and speed, the system will trigger an alarm having the ability to reduce false and nuisance alarms caused by birds and other non-invasive elements.

Fence Mounted Acoustic Sensors

There are several sensors of this type available. When attached to the fence either acoustic, geophonic, seismic or fibre optic cable scan frequencies associated with an intruder attempting to cut, climb or tamper with a fence. This monitoring data coupled with timing and counting circuits enable fences to become an integral part of a perimeter security system.

Mono and Bi-Static Microwave Sensors

Microwaves are a volumetric beam sensor designed to detect movement through Doppler shift or pulse technology within a predetermined volume. Microwave is probably one of the more common technologies used in a perimeter and one of the most cost effective. Microwaves typically comprise of transmit and receive elements (bi-static); however, microwave transceivers (mono-static) are available for outdoor use.

Pulsed Infra Red (PIR)

PIR or Photo Electric (PE) beams utilise an infra red laser to send a pulsed beam to a receiver some distance away, should this beam be broken then an alarm is generated.

Ported or Leaky Coax

A covert terrain following sensor; buried cable(s) generates an electronic field above ground to about 2 metres, which will detect any intruder entering the detection zone.

Taut Wire

These passive systems generally comprise multiple horizontal strands of barbed wire, each connected to a strain gauge that measures any deflection of the wires. Where deflection is outside a pre-determined tolerance an alarm is generated.

Capacitance Fence Systems

Centre balanced capacitance systems typically consist of a number of horizontal conductive wires, isolated from earth. They form a physical barrier and at the same time generate a capacitance field (100mm approx) around the individual strands that will detect any intruder that enters the detection field.

Lethal and Non-lethal Electric Fences

A basic non-lethal electric fence uses a low voltage, low frequency AC current to administer a substantial jolt of electricity to any potential intruder who touches the fence. High voltage, high frequency electric fences can deliver a lethal shock.

The above is a summary of systems which can be used in perimeter protection, there are other systems available, and all should be considered when designing a perimeter strategy, due to the unique nature of each perimeter and its requirements.