Introduction
Perimeter Intruder Detection Systems (PIDS) act as a technology force multiplier, they keep a constant watch on a site’s perimeter and offer the opportunity for early detection of an attack.
PIDS systems are normally designed to work in a specific scenario, NPSA assure PIDS into the following categories.
For an in depth guide to PIDS, please read Perimeter Intrusion Detection Systems (PIDS) guidance
Perimeter Intruder Detection Systems, or PIDS, are used to detect intruders attempting to gainillegal entry onto or into your site.
Ideally, you will have a perimeter surrounding your site, which traditionally takes the form of a fence or other barrier.
This may also include a sterile zone, depending on your level of security requirement.
PIDS are deployed at your perimeter so that a maximum early warning is enabled.
As with all detection systems, all alarms need to be verified by the Security Control Room, or SCR.
As PIDS are prone to false alarms, all alarms need to be verified quickly, before any security response is initiated. False alarms can be caused by factors such as weather, animals or a technical failure within the PIDS itself.
Alarms are typically verified through the use of CCTV video surveillance. The SCR uses CCTV to view the area surrounding the alerting PIDS and confirm whether false or not.
Perimeter lighting may also be required to support the CCTV and aid the SCR operators in verifying alarms.
The aim when commissioning a PIDS system is to get the right balance between high detection and low false alarm rates.
If the sensitivity of the PIDS is set too high, there may be too many alarms.
But if the sensitivity is set too low, the site may be breached without security personnel being aware.
It should be noted that no PIDS would achieve zero false alarms.
An acceptable false alarm rate is five alarms per day, per kilometer in good weather.
This rate will rise in extreme weather conditions.
There are a number of different PIDS modalities that you can choose to implement on your site.
Typically, these are:
- Barrier Mounted PIDS, deployed or integrated with the fence
- or physical barrier around your site.
- Electric Fences.
These are normally deployed in conjunction within an already existing host fence or barrier.
Ground Based PIDS.
Deployed below the ground, typically behind a barrier or fence.
Freestanding PIDS.
Deployed independently from any physical barriers on your site.
These are typically placed behind any barriers to create a virtual barrier.
Rapidly deployable PIDS.
These use the same technology as freestanding PIDS, and provide quick and temporary cover for a site, when it's not practical or affordable to deploy a permanent PIDS system.
The major benefits of deploying PIDS as part of your security measures, is that it gives you the earliest possible detection for any intrusion attempt, and allows your Security Control Room to initiate a quick response.
PIDS detect intruders.
They do not offer any delay measures themselves, and they work best when combined with physical security measures such as fences, walls or other barriers.
Deploying PIDS on your site adds a layer of security that allows early detection of any intrusion attempt.
In order to build effective security across all of your sites.
They should be deployed in conjunction with other security measures such as CCTV and Access Controls Systems.
Barrier-mounted PIDS
Barrier-mounted PIDS are attached to a barrier such as a high security fence; they work in conjunction with the fence to offer detection and delay. Barrier-mounter PIDS may consist of:
- Microphonic cable systems – generally use piezoelectric cable attached to the fabric of a fence to detect the vibrations caused by an intruder breaching the fence.
- Geophones and point sensor systems – comprise a series of low frequency microphones or accelerometers attached to the fence structure to detect the vibrations caused by an intruder breaching the fence.
- Electric fence systems – comprise multiple horizontal wires which are electrified with non- lethal high voltage and generate an alarm if the cables are cut or the voltage is earthed by either touching the wires together or by one of the cables touching the metallic supporting structure or the host fence. Where an existing fence is to be used as the host fence its strength (including foundations) should be considered.
Barrier Mounted Perimeter Intruder Detection Systems, or PIDS, are a type of security measure deployed to detect intruders into or onto your sites.
Ideally, you will have a perimeter surrounding your sites, which traditionally takes the form of a fence or other barrier.
This may also include a sterile zone, depending on your level of security requirement.
PIDS are deployed at your sites perimeter. This provides the earliest possible warning to your Security Control Room, or SCR, of a potential intrusion.
One category of PIDS is Barrier Mounted, which are mounted on the fence or other physical barrier around your site.
Barrier Mounted PIDS detect intruders. They do not offer any delay measures themselves, though they may act as a deterrent.
It is the host barrier that provides the delay during any intrusion attempt.
An attempted intrusion will trigger Barrier Mounted PIDS while the attacker is still outside the site's perimeter.
This delay allows security the time to verify the alarm and issue the relevant security response.
A Barrier Mounted PIDS system must always be mounted on the secure side of the site's perimeter fence. This makes it inaccessible to an intruder. If there is a sterile zone implemented at a site and the outer fence is out of a site's control, for example, it's next to a publicly accessible area; it is advised that PIDS should be installed on the secure side of the inner fence.
In this case, the outer fence is used purely as demarcation rather than as a security measure.
Doing this reduces the chances of false alarms and interference from the outside world.
However, by placing the PIDS on the fence, the effectiveness of your sterile zone could be undermined as there is less delay time to hinder an intrusion attempt, leaving the intruder to only need to breach a single fence before gaining access to the site.
As with all detection systems, some form of verification should be in place to confirm an alarm.
Typically, this will be in the form of CCTV video surveillance.
The SCR uses CCTV to view the area surrounding the alerting PIDS.
A perimeter lighting scheme may be required to support the video surveillance system.
With Barrier Mounted PIDS, the barrier itself supports the system, offering some limited protection against tampering by hindering an attacker’s access to the PIDS.
Each technology of Barrier Mounted PIDS will have its own specific barrier requirements and should always be deployed on the fence or barrier they were designed for.
If a fence is too rigid in its construction, a Barrier Mounted PIDS will not detect vibrations generated during an attack.
And if too flexible, false alarms may be generated by environmental factors such as wind or rain.
Not all PIDS will work on all barrier types. Matching PIDS to barrier type is paramount in creating a successful security system.
Barrier Mounted PIDS effectively become part of the barrier system, so matching the PIDS with the correct barrier is key, as they work in combination.
For example, metal weld mesh fences help transmit the vibrations across them, to be detected by sensor cable PIDS.
All Barrier Mounted PIDS can be prone to false alarms, generated by weather conditions, accidental contact by wildlife, humans, blown debris, or overgrown vegetation at the fence line. Climbing attacks can be hard to detect. The height of the barrier and the choice of fence
topping are important factors to consider.
By creating a difficult fence to climb over, more noise and vibration may be generated during an intrusion attempt, increasing the chance of the PIDS alarming.
PIDS are deployed in zones around your perimeter so that an alarm specific location can be identified and easily verified.
Careful consideration of CCTV placement and perimeter lighting is required when designing these zones, so that accurate information is relayed to the Security Control Room.
Ensuring your PIDS are resilient in the event of any power outage is essential.
A backup power source such as an Uninterruptible Power Supply, UPS, is recommended.
There are several types of Barrier Mounted PIDS available.
Vibration Sensor Cables and Point Sensors are the most common type of Barrier Mounted PIDS.
Sensor cables or point sensors are installed across the length of your perimeter fence, and they detect vibrations caused by an intruder attempting to climb or cut a fence.
Typical Barrier Mounted Sensor technologies include micro sonic and fibre optic cables, accelerometer-based points, sensors and electrical circuit systems.
Microphonic PIDS listen for different frequencies associated with climbing or cutting intrusion attempts but can suffer from high false alarm rates caused by adverse weather, such as heavy winds or rain.
Fibre optic systems measure the variation in light through their fibre cause. Increased vibration during any intrusion attempts disrupts this light and triggers an alarm.
Fibre optic systems are seen commonly on sites that cover large perimeters.
Accelerometer-based sensors are placed at strategic locations along a fence line, and can provide a very accurate location of any attempted intrusion.
Electrical circuit systems commonly known as Electric Fence PIDS, work with the site's barriers, passing an electric current through a wire system.
If the wire is forced to be grounded, for example, by a climbing attempt, or if an intruder uses certain tools to compromise the fence, the circuit will short and trigger the alarm.
Barrier Mounted PIDS are an effective method of detecting an intruder at a site's perimeter.
It is important that the correct balance between detection sensitivity and false alarming is achieved.
If sensitivity of the PIDS is set too high, there may be too many alarms to verify.
But if the sensitivity is set too low, the site may be compromised without security personnel being aware.
It should be remembered that no PIDS will achieve zero false alarms.
Barrier Mounted PIDS need to work in conjunction with your existing barriers, and take into account your site's geography and security challenges.
Barrier Mounted PIDS can form an important component of any security system, but they only provide one protective layer of security around your site.
They should be deployed in conjunction with other security measures, such as Access Control Systems, onsite security officers, and CCTV, to create a multi-layered security system.
This will keep intruders far away from your protected information, and your assets, and ensure your site is secure.
Electric Fence Perimeter Intruder Detection System, or PIDS, are a type of security measure deployed to detect intruders into or onto your sites.
Ideally, you will have a perimeter surrounding your site, which traditionally takes the form
of a fence or other barrier.
This may also include a sterile zone, depending on your level of security requirement.
PIDS are deployed at your sites perimeter.
This provides the earliest possible warning to your Security Control Room of a potential intrusion.
Electric Fences fall under the category of Barrier Mounted PIDS, as they are normally attached to, or near, a fence or barrier.
They are traditionally viewed as an aggressive people or animal deterrent and are often seen in agricultural environments.
In physical security terms, the primary function of an electric fence is to act as a detection system, with the physical deterrent being an additional benefit.
Electric fences can be either full height, deployed behind an existing barrier, or as a topping, added at the top of an existing barrier or fence.
By shorting or grounding electrical wires, an intruder triggers a detection alert when either climbing or cutting, for security personnel to verify.
The electrical circuit is of a high voltage, but low current, so it can give a painful shock to any intruders.
Even though the electric fence is intimidating, and a visible security presence, it can act as a deterrent.
However, in reality, it offers little delay to an intruder.
Electric fences perform well in bad weather, and can offer a low false alarm rate, with good detection performance against climbing and penetration intrusion attempts.
But they need a good maintenance schedule so as to maintain wire tension, remove any undergrowth near the fences, and to deal with any other environmental issues such as salt deposits, if deployed near the sea.
They can be deployed in a full fence configuration, or as a fence topping.
If deployed in a full fence configuration, wire tension is important. If too loose, then intruders may be able to pull wires apart, or manipulate fixings to create a gap to squeeze through.
Electric fences can be deployed
in a number of ways:
The electric fence is placed on the inside of your perimeter fence or barrier.
The main disadvantage of this configuration is that detection will only be made after the host fence has been penetrated.
An intruder could have unlimited time in getting through your site's perimeter fence.
Sites will be reliant solely on CCTV monitoring, or physical security patrols, capturing an intrusion attempt in progress.
If an electric fence is freestanding behind an existing barrier, the creation of entrapment areas needs to be avoided.
The gap between the electric fence and the outer fence should be either less than 20 centimetres, or more than a meter.
This avoids an intruder becoming trapped between the electric fence and the barrier, and being continually shocked.
This deployment offers good deterrence, and post-detection delay.
The alert is sent when the intruder approaches and interacts with the electric fence, and then has to defeat the perimeter fence or barrier, giving security time to react.
In this configuration, the fence must be in a sterile zone to limit accidental contact with the electrified fence by members of the public. Electrified toppings to existing fences are a good deterrent against climb-over intrusion attempts.
With them being installed at height, they present less risk of accidental contact to the general public.
Installed in this configuration, a separate Barrier Mounted PIDS is essential to mitigate the risk of cutting of the fence or barrier it is attached to.
In all scenarios, warning signs should be prominently displayed on all electric fences, spacings not exceeding ten meters.
As with all detection systems, some form of verification should be in place to confirm an alarm activation.
Typically, this will be in the form of CCTV systems, also known as video surveillance systems.
A perimeter lighting scheme may be required to support the video surveillance system.
Electric fences are an effective method of detecting an intruder at a site's perimeter.
They provide good detection capability, whilst also providing an effective deterrent, due to provision of non-lethal electric shock when touched.
They should always be used in conjunction with a barrier to provide a period of delay during an intrusion attempt.
They do require a good maintenance schedule based on a site's local environment and weather conditions. It is important that the correct balance between detection sensitivity and false alarming is achieved.
The aim when commissioning a PIDS is to get the right balance between high detection and low false alarm rates.
If the sensitivity of the PIDS is set too high, there may be too many alarms to verify.
But if the sensitivity is set too low, the site may be compromised without security personnel being aware.
It should be noted that no PIDS will achieve zero false alarms.
Electric fence PIDS are an important component of any security system, but they only form one protective layer of security on your site.
They should be deployed in conjunction with other security measures, such as Access Control Systems, onsite security officers, and CCTV, to create a multi-layered security system.
This will keep intruders far away from your protected information and your assets, and ensure your site is secure.
Ground-based PIDS
Ground-based PIDS are buried in the ground and may or may not be deployed alongside a fence, they may consist of:
- Ported coaxial cable/leaky feeder systems – comprise leaky feeder cable(s) to create a radio frequency electromagnetic field which detects the presence of a moving intruder by the change created in that field.
- Microphonic cable systems - generally use piezoelectric cable to detect the vibrations caused by an intruder moving across the zone.
- Fluid filled tubes – comprise two tubes filled with fluid and detect the presence of an intruder by the pressure exerted upon them through the ground.
Detection Systems, or PIDS, are a type of security measure deployed to detect intruders into or onto your site.
Ideally, you will have a perimeter surrounding your site, which traditionally takes the form of a fence or other barrier.
This may also include a sterile zone, depending on your level of security requirement.
PIDS are deployed at your site’s perimeter. This provides the earliest possible warning to your Security Control Room of a potential intrusion.
One category of PIDS is Ground Based.
One category of PIDS is Ground Based, as their name implies. As their name implies, Ground Based PIDS are installed below ground level, giving you an invisible barrier of detection around your site.
Using pressure sensitive seismic or radio frequency based sensors, they detect above-ground activity, such as footsteps, digging or vehicle traffic, without the intruder being aware.
Ground Based PIDS detect intruders.
They do not offer any delay measures themselves.
They are effective when deployed in conjunction with physical security measures, such as fences, walls, or other barriers; which provide some delay during an intruder attempt.
Ground Based PIDS should ideally be installed within a site sterile zone, having compromised the outer fence.
An intruder will unknowingly trigger the system and alert the SCR.
The intruder still has to compromise the inner fence, unaware that they have been detected, allowing the security team time to verify the alarm and issue the relevant security response.
By placing it in your sterile zone, you can minimize the number of false alarms caused by factors such as debris, animals and humans.
As with all detection systems, all alarms need to be verified by the Security Control Room or SCR, and as PIDS are prone to false alarms, all alarms need to be verified quickly before any security response is initiated.
Ground Based PIDS should be installed in the burial medium that they are designed for.
Installation in an incorrect burial medium could result in an increased false
alarm rate and a decreased detection rate, so following manufacturer's installation
specifications is essential.
All Ground Based PIDS have the benefits of being invisible to intruders, and can be installed in undulating ground, which might be unsuitable for other types of PIDS.
They follow the lay of the land and can be used to protect any natural hiding places in the terrain where an intruder would want to hide.
They are a system which is extremely difficult to tamper with and are hard to defeat without insider information.
However, they are a costly measure due to the ground works required for installation and are considered a long term solution, as once buried, they can't be moved or redeployed.
They can struggle to differentiate between animal and human activity, and do not work optimally when placed near to water, or the water table.
They are sensitive to seasonal changes in the weather.
They can also be affected by nature over time, such as tree roots, and changing barrier foundations affecting the ground they are buried in.
Microphonic or Vibration Based PIDS systems particularly struggle to discriminate between animals and humans, which can cause false alarms.
Ground based PIDS are set up in zones around your perimeter, so that an intrusion attempt’s specific location can be easily identified.
Careful consideration of camera placement and lighting is required when setting up zones, so that accurate information is relayed to the Security Control Room in order for alarm verification to be achieved.
Ensuring your PIDS are resilient in the event of a power outage to avoid loss of detection capability around the site's perimeter is essential.
A backup source such as an Uninterruptible Power Supply, UPS, is recommended.
There are several types of Ground Based PIDS:
Microphonic or Vibration Based PIDS are detectors or detector cables, buried in the ground that respond to vibrations caused by the impact of footfall or vehicles above them. But they can cause false alarm due to spurious noise around them, such as passing trains or moving tree roots due to high winds.
Fluid Filled Tubes PIDS are tubes filled with antifreeze.
An intruder steps on ground above the tube, changing the pressure inside and triggering an alarm.
As these are deployed outside, antifreeze is used to combat falls in temperature.
They can also false alarm due to tree roots or moving fence foundations in extreme weather.
Ported Coaxial Cable PIDS, or leaky feeder systems as they are sometimes known, leak radio waves from a pair of cables installed underground.
An alarm is triggered when an intruder interferes with those radio waves.
Rapidly moving water flooding or fast draining soil can cause false alarms.
Ground Based PIDS offer an invisible detection barrier to protect your site's perimeter.
They work well on sites with undulating perimeters, but care needs to be taken as to the ground they are installed in, and the surrounding environment.
Sensitivity settings are key to your Ground Based PIDS effectiveness, and commissioning & testing is important to find the correct settings for your environment.
It is important that the correct balance between detection sensitivity and false alarming is achieved.
If the sensitivity of the PIDS is set too high, there may be too many alarms to verify. But if the sensitivity is set too low, the site may be compromised without security personnel being aware.
It should be noted that no PIDS will achieve zero false alarms. Ground Based PIDS are an important component of any security system, but they only form one protective layer of security on your site.
They should be deployed in conjunction with other security measures, such as Access Control Systems, on-site security officers, and CCTV, to create a multi-layered security system.
This will keep intruders far away from your protected information and your assets, and ensure your site is secure.
Free-standing PIDS
Free-standing PIDS cover an area above ground and may or may not be deployed alongside a fence. Free-standing PIDS may use:
- Active infra-red systems – comprise a transmitter and receiver module and detect the presence of an intruder by the disruption of one or more infrared beams.
- Monostatic/doppler microwave system - detects the presence of a moving intruder by responding to the reflection of radio waves.
- Bistatic microwave system - detects the presence of a moving intruder by responding to the disruption of radio waves.
- Passive Infra Red system - detects the presence of a moving intruder by responding to the infra red (heat) signature generated by the human body.
Freestanding Perimeter Intruder Detection Systems, or PIDS, are a type of security measure
deployed to detect intruders into or onto your site.
Ideally, you will have a perimeter surrounding your site, which traditionally takes the form of a fence or other barrier.
This may also include a sterile zone, depending on your level of security requirement.
PIDS are deployed at your site’s perimeter.
This provides the earliest possible warning to your Security Control Room of a potential intrusion.
One category of PIDS is Freestanding. As their name implies, Freestanding PIDS are deployed above ground in isolation to the barriers of your site and create a virtual rather than physical barrier.
Using infrared, microwave or laser based technologies, they create a virtual barrier, that, when breached, sends an alert to your Security Control Room.
Freestanding PIDS detect intruders.
They do not offer any delay measures themselves.
They are effective when deployed in conjunction with physical security measures, such as fences, walls or other barriers, which provide some delay during an intruder attempt.
The best deployment location for any Freestanding PIDS is in a sterile zone on your site, behind a physical barrier where they are protected from intrusion attempts, unless vulnerable to false alarms.
They can be vulnerable to tampering, if located in positions where the system can be reached before an alert is generated.
When placed in a sterile zone, they alert when an intruder has compromised the outer fence and triggered the system.
The intruder still has to compromise the inner fence, allowing the security team the time to verify the alarm, and issue the relevant security response.
Being placed in a sterile zone minimizes the false alarm rate, as objects such as debris, animals and humans are excluded from this area.
As with all detection systems, some form of verification should be in place to confirm an alarm activation.
Typically, this will be in the form of CCTV systems, also known as video surveillance systems.
A perimeter lighting scheme may be required to support the video surveillance system.
When choosing to deploy Freestanding PIDS around your site, the key factors to consider are where they will be placed, and what environment is around them.
They should be used on flat ground and in environments that will maximize their performance and minimize false alarms.
Freestanding PIDS need to be protected from intrusion attempts as they can be highly visible, but as a visible security measure, they can act as a deterrent.
Correct sighting is essential so as to avoid systems being used as a climbing aid for any intruders.
With Freestanding PIDS, a system's performance is very much dependent on the technology chosen.
Care should be taken to ensure it is appropriate for the specific site's environment.
Depending on the technology chosen, they are sensitive to certain weather conditions, such as fog and heavy rain, which can have a detrimental effect on performance.
Careful consideration of camera placement and lighting is required so that accurate information is relayed to the Security Control Room in order for alarm verification to be achieved.
Ensuring your PIDS is resilient in the event of a power outage to avoid loss of detection capability around a site's perimeter is essential.
A backup power source, such as an Uninterruptible Power Supply UPS, is recommended.
There are several types
of Freestanding PIDS:
Non-visible IR beams travel between two towers. When an intruder walks between the towers, they break the beams and trigger the alarm.
This technology can have reduced detection or high false alarm rates in fog, snow and heavy rain. Clear line of sight between transmitter and receiver is required, and they should be deployed on flat, consistent ground. If used on undulating ground, dead spots may be unintentionally created for an intruder to use, to evade detection.
Discriminating between an animal, bird or a human is a known issue, as is swaying vegetation.
So keeping the detection area clear is essential.
PIRs use filters within the sensor to divide their deployment area into different detection areas, and monitor any changes of temperature within that area.
The PIR will register the difference between any intruder and the background, and an alarm will signal.
When used externally, PIRs generally suffer from poor detection and high false alarm rates, as the wide and rapid variation in temperature, means these systems will always struggle to perform accurately outdoors.
A microwave field is generated between a sending and receiving tower. This field is sensitive to movement. When an intruder walks through and disturbs this field, it causes a reduction in its strength, and the alarm is signalled.
Microwave systems typically need a long, straight and clear line of sight, ideally in a sterile zone, to ensure no part of the detection field is unintentionally blocked. Unfortunately, there are dead zones where no detection occurs near the transmitter and receiver.
To counter this, Bistatic Microwaves must be deployed with an overlap configuration.
Like with Active Infrared PIDS, discriminating between animal, human or other, such as swaying vegetation, is difficult.
Keeping the detection area clear is essential to prevent false alarms.
Microwave systems perform better on undulating ground, than active IR systems.
These systems can be affected by wind, causing blown debris or non intruder objects to cross the fields, causing false alarms.
Compared to Active Infrared Systems, they tend to be more reliable in bad weather conditions.
The detector sends out a microwave signal. This signal bounces off objects in the deployment area and returns to the detector.
Intruders disturb this field and signal the alarm. Doppler microwaves suffer from the same issues as Bistatic Microwave systems. Freestanding PIDS can be an effective method of detecting an intruder at a site’s perimeter. Care needs to be taken when selecting a specific technology, as their effectiveness is heavily dependent on the site's environment and weather conditions.
It is important that the correct balance between detection sensitivity and false alarming is achieved. The aim, when commissioning a PIDS, is to get the right balance between high detection and low false alarm rates. If the sensitivity of the PIDS is set too high, there may be too many false alarms to verify.
But if the sensitivity is set too low, the site may be compromised without security personnel being aware.
It should be remembered that no PIDS would achieve zero false alarms.
Freestanding PIDS are an important component of any site-wide security system, but they only form one protective layer of security on your site.
They should be deployed in conjunction with other security measures, such as Access Control Systems, onsite security officers, and CCTV, to create a multi-layered security system.
This will keep intruders far away from your protected information and your assets, and ensure your site is secure.
Rapidly-deployable detection systems
Rapidly deployable detection systems can operate using any of the above detection methods. A rapidly deployable system is defined as one which can be deployed by two people within a short period of time.
Rapidly-deployable systems should not be used for more than a two week period without the system being re-commissioned.
Wide-area detection systems
Unlike free-standing PIDS which are designed to detect intrusion along a perimeter, wide-area detection systems cover a large area within and external to a site perimeter, allowing for detection and tracking within an open space.
PIDS Evaluation Schemes
NPSA runs various functional evaluation schemes for perimeter intrusion detection products. This page describes the schemes and the process that manufacturers should follow for product submission.
