Keeping the Bad Guys Out

Aug. 27, 2014
Perimeter intrusion detection systems remain a dominant technology for A&Es in almost every market

As a huge Game of Thrones fan, I can’t help but admire the measures that the monarchs in imaginary Westeros take to fend off their enemies – the mighty castle fortifications, the moats,  and most formidable, “The Wall” that prevents the terrifying white walkers from invading.

Yet those defenses lack an important element in securing critical facilities (or medieval castles, for that matter)—a Perimeter Intrusion Detection System (PIDS) that provides early-enough notification of an intrusion before it occurs, so there’s enough time to prevent the intruders from actually causing harm.

PIDS are nothing new. In different forms, they have been used for many decades, with varying rates of success. In this article I’d like to review the different PID technologies currently available, and provide recommendations based on the type and size of the protected facility.

The Challenges

Like any other security system, PIDS face a number of challenges:

  • Successfully detect perimeter intrusions, regardless of deliberate disturbances – The PID system needs to be sensitive enough to detect human or vehicular intrusion, and it should not be affected by the intruders’ attempts to impede its operation (for example, by flooding the area with electromagnetic radiation).
  • Minimize nuisance alarms, caused by environmental factors such as fog, rain, snow, wind and wind-blown debris, and extreme temperature, as well as system-generated false alarms.
  • Immunity to sabotage – the PID system should not only detect (and report) sabotage attempts, but also withstand such attempts.
  • Adherence to security regulations in different industries – for example standards set by the nuclear regulatory commission, the CFATS anti-terrorism for the chemical industry, the National Safe-Skies Alliance for the aviation industry, and others.
  • Minimize total cost of ownership (including installation and operation) over the entire lifespan of the system.

Specifying the right PID technology for a specific facility, therefore, depends heavily on the environment it operates in, as well as the size of the facility and the type of detection required. In the following review I’ll measure each technology against these challenges within different environments.

Non-Barrier PIDS

The most basic distinction between PID technologies is between infrared and microwave sensor systems, that are not incorporated into, or make up a physical barrier; and barrier-based systems, which detect disturbances along a cable or wire, which can be installed on a fence, buried to detect ground movement, or set up as a standalone barrier.

Infrared Beam PIDS

Probably the most commonly-known type of PIDS (at least in popular culture), infrared beam systems are composed of accurately-positioned transmitters and receivers of non-visible light frequencies. (Unlike the movies, where you see Tom Cruise dancing between strings of visible red light in Mission Impossible, in real life they are colorless).

This type of PIDS is very popular and quite effective in small indoor applications. In outdoor installations, infrared beams generally generate a high rate of nuisance alarms caused by weather conditions (fog, rain, airborne sand and debris, etc.) In addition, the sensitivity of the system is affected by the length of the beam, since it degrades as it passes through the air.

Passive infrared PIDS

Passive infrared PIDS can be used successfully in smaller controlled-environment indoor areas. These relatively inexpensive volumetric systems basically detect temperature changes in the infrared frequency range within a volume of air monitored by an IR sensor (hence the term “volumetric”, as opposed to infrared beams that detect disturbances along thin, defined beams.) Passive infrared PIDS naturally have a smaller detection range, and they share the innate disadvantages of infrared beam systems. For this reason they are often coupled with another volumetric system, such as Doppler microwave technology.

Microwave Beam-Based PIDS

Another type of volumetric PIDS, microwave beam-based systems are more suitable for outdoor use than infrared systems. Similar to infrared beam technologies, they also use a transmitter and a receiver of microwave-frequency radiation, but in microwave systems a single transmitter-receiver set can detect motion in a large volume of air, due to the non-linear nature of microwave radiation. Microwave systems are suitable for areas that lack a physical barrier, or alongside barrier-based systems.

However, as the performance of microwave PIDS is very much affected by weather conditions (fog, precipitation, wind, air clarity) and deliberate (malicious) electromagnetic interference, they tend to have an intrinsically high level of nuisance alarms. Therefore, in critical installations, microwave-based systems should not be used as a standalone PIDS.

Video Content Analytics

Another non-barrier technology is video content analytics, which detects changes in the pixel content of a video stream. Video content analytics systems are very good at detecting movement based on set criteria for size, direction and speed of movement and other visual characteristics; however they become practically useless in low-visibility conditions, and therefore should never be used as a standalone PIDS, especially in critical installations.

Barrier-based systems

Barrier-based PIDS detect intrusion by measuring energy changes along cables and wires, for each respective energy carrying technology. Barrier-based PIDS can be either installed on a physical barrier (typically a fence), comprise a barrier in their own right, or buried around the perimeter.

Compared to infrared- and microwave-based PIDS, barrier-based PIDS are suitable for outdoor use because they are generally much less susceptible to environmental conditions.

Taut-Wire Sensor PIDS

The clearest example of a barrier-based PIDS is a taut-wire sensor system, which measures minute changes in tension along an array of controlled-tension steel wires. This means that the system will not detect non-direct disturbances (such as a person walking along the taut-wire array), but will detect, at a very high probability, any contact with it, with a low nuisance alarm rate.

Despite their high detection rate, taut-wire systems are quite uncommon since they are the most expensive to install. In addition, their detection and nuisance rates are very much dependent on accurate and continuous maintenance.

The two more common barrier-based PIDS use microphonic coaxial electric cables and fiber optic cables.

Microphonic Cable PIDS

Microphonic cable PIDS use a specially-purposed conductive sensor cable that converts vibration into an electric current to produce an alarm.

The two common technologies in microphonic cables are piezoelectric cables, where the current is generated by applying pressure to a semi-conductor polymer; and triboelectric (coupled) cables, which generate current by rubbing two conducting materials.

Microphonic cable systems provide an adequate, cost-effective PID solution for installations with relatively small perimeters and short detection zones. However, as with all conductive cables, they have a major vulnerability: they run a carrier electric current, which may cause ignition in combustible industrial environments; and they conduct unwanted electric currents. Microphonic sensor cables are susceptible to malicious electromagnetic interference which can impair the PID system’s detection capability; and even worst, long electrical cables attached to fences actually attract lightning, which can destroy the system altogether.

Microphonic cable PIDS have a relatively short service life, usually around five to seven years, and they incur relatively high annual maintenance costs.

Fiber Optic-based PIDS

This newer technology has become the preferred PID solution for medium- and large-scale installations with over a few hundred feet of protected perimeter, either along a fence and/or buried along the perimeter to detect ground movement.

Currently around 35-40 percent of new medium-to-large installations (typically industrial, infrastructure and national security) use fiber optic-based PIDS, and certain industries like oil, gas and chemical have altogether embraced fiber optic PIDS as the technology of choice. Similarly, the electric power generation industry has been displaying increasing interest, because of fiber optic PIDS’ immunity to electromagnetic energy and the very long service life of the system.

Fiber optic sensor cables are capable of detecting minute changes in light-flow (the amount of light carried by the cable) caused by the smallest of disturbances over a very long cable. (Some fiber optic PIDS are able to detect even a small bird landing on a fence, although they’d be configured to eliminate non-human intrusion detections.) 

Since fiber optic cables are not electrically conductive, they overcome the vulnerabilities of microphonic cables—they are immune to electromagnetic interference, so an intrusion cannot be “masked” using an electromagnetic pulse device (and would not be affected by surges of electromagnetic radiation in a power plant or substation). Fiber optic cables do not attract lightning; the cable does not consist of metal or any other corrodible material so it doesn’t degrade in quality or functionality; and little or no maintenance is required over the system’s operating service life, usually 20-plus years.

Another advantage of fiber optic PIDS is that the cable itself can be used for communication, for the PIDS and for other integrated physical security systems (including other PIDS technologies, video surveillance along the perimeter and other security systems—some high-security applications, such as nuclear facilities, Level-1 military facilities, and some prison applications, have regulatory requirements that define parallel non-related security layers, i.e. a non-fiber optic based security system.)

Fiber optic PIDS do have one disadvantage compared to microphonic (coaxial) technologies: a higher base (minimum) system cost, due to the optical electronic components that are more costly than electrically-based sensors (whose base cost is lower, but installation is much more expensive). For this reason, fiber optic intrusion detection technology has been adapted mostly by medium- and large-scale installations, where the total cost of ownership is offset by the system’s longer lifespan, usually four to five times of microphonic cable PIDS. This factor actually brings the total cost of point-location fiber optic systems below that of electrically conductive sensors.

In smaller and less-critical installations, such as remote power substations, penetration is still slow, but is expected to increase in the coming years.

If you intend to specify a fiber optic PID system for an upcoming project, here are a few considerations:

  • Is the system immune to severing the cable? Look for bi-directional fiber optic PIDS which can withstand cutting the cable within a segment connected to a single controller.
  • Penetration point accuracy – can the PIDS report where the intrusion had occurred, and how accurately? This factor is crucial for minimizing response time to intrusion incidents.
  • Can the system accurately detect simultaneous disturbances? This is extremely important, because otherwise a decoy intrusion attempt would divert attention from the actual intrusion.
  • Nuisance alarm rate – while no system can assure a zero nuisance alarm rate, some systems do way better than others in filtering out environmental disturbances. Check the rating of different systems for this criterion.
  • Does the fiber optic PIDS require power along the perimeter? Some systems don’t—making them completely inert, thus safe for operation in combustible environments such as gas production facilities (compliant with Category-1 Division-1 & 2 safety standards).
  • Type of fiber optic cable used – some PIDS vendors use off-the-shelf fiber optic communication cables, while others require purchasing their proprietary fiber optic PID sensor cables. Based on my experience, proprietary cables do not offer any functional advantage over off-the-shelf cables; however they are much more expensive both during installation and maintenance (if a cable segment needs to be replaced). Also, for overseas installations, using off-the-shelf cables can basically eliminate shipping costs and there are no import tariffs.


A PID system should be a part of the security mix in all critical facilities and infrastructures in a wide range of industries. However, understanding the way the different systems work is crucial to choosing the right type.

For indoor, controlled-environment applications, infrared- or microwave-based PIDS can provide an adequate intrusion detection solution. Microwave systems can also be used in non-critical outdoor installations, usually as a secondary PID system. 

For outdoor installations, today’s fiber optic PIDS are advantageous in every way to microphonic systems except for base cost, making them suitable mostly for medium-to-large systems. However, any decision should take into account the longer life-span and much lower maintenance cost of fiber optic PID systems.

About the Author:

Ayel Vogel is president of AMID Strategies. He has more than 20 years of sales, marketing and management experience in the homeland security industry. For more information, visit