Perimeter Intruder Detection

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.