Home System Design Sensing Options at the Perimeter

Sensing Options at the Perimeter

by Benchmark

With any secure site, protection starts at the perimeter. This is the first point at which outsiders – whether guests or intruders – make a decision to enter a site. Regardless of whether the perimeter presents a physical barrier, it should provide a definitive demarkation that makes it clear and obvious that the site is private. This also allows the start of effective monitoring for people, but which technology is best suited to perimeter monitoring?

For many years the main focus with regard to site protection, with its mainstay of intruder alarms, was the detection of persons once they had entered secured buildings. Activity at the perimeter or in external areas within the perimeter was largely used to trigger secondary systems (the definition of secondary systems being elements of the solution that do not elicit a response, unless by on-site personnel), such as security lighting, video surveillance or audible challenges.

This approach was largely dictated by the insistence of insurers that businesses and organisations had a police first response, and the ACPO Policy’s reluctance to include external detection. While BS8418 did raise more possibilities for detector-activated video surveillance, the focus remained on internal intruder detection.

Such an approach has upsides and downsides. With regard to positives, internal spaces are typically more stable and as such represent a less challenging environment for reliable and efficient detection. Also, when internal spaces are secure (i.e. the alarm is set) any genuine movement created by people is an exception and an alarm should be generated. The ability to treat the entire space as a sterile zone makes system design a simpler task.

The downside is obvious: in order for an internal detection system to be effective, an intruder will have forced an entry to a secure building. As any end user who has suffered a break-in will know, this means there will inevitably be damage to the building fabric which will necessitate repairs. Also, a fleeing intruder will take anything of value to hand, so there is also the potential of some degree of loss.

The end customer’s preference will always be to detect intruders, and take some form of action, at the earliest point possible, and this often means at the perimeter. In many cases, police first response is no longer the ultimate consideration in security.

Firstly, because of constraints on budgets, police first response is often unlikely. While it was never a guarantee, the likelihood of the police attending an alarm activation in a timely fashion is negligible, with some sites unlikely to get more than a follow-up visit to issue a crime number, often a day or so after an alarm. End users know this, as do insurers, and as a result many businesses are seeking systems that empower them to take action, using internal intruder detection as a last (but important) layer of protection.

By detecting intrusion at the earliest opportunity, end users are enabling themselves, and their partners, to be able to take actions before any damage is caused, or the intruder gains access to assets of value. It is the early warning that perimeter detection gives which users often value.

For example, Benchmark knows of one industrial estate where the vast majority of businesses have alarm systems that elicit a police first response. Because the site is remote, a history of break-ins resulted in insurers stipulating the need for graded alarm systems. This did not impact on the level of crime.

However, when the businesses got together, added perimeter detection for early warnings and contracted a private security firm to offer response, crime levels at the site fell significantly.

When considering perimeter detection, there are a variety of options. However, if looking for standalone, flexible and cost-effective options, the decision falls between external detection devices and thermal imaging using IVA.

External sensors

External detectors have become increasingly stable, and today they offer a cost-effective and reliable method of perimeter detection. As manufacturers invest R&D resources into creating credible and robust external devices, so the options have become more specialised.

Today’s external detection devices are a far cry from the units of a few years ago. In the past the approach to external detection was often to put a dual technology sensor in a weathproof housing, increase the pulse count and hope for the best. Because the devices weren’t used in graded solutions, they often switched supplementary systems such as lighting. However, the value of perimeter detection has always been recognised by end users, and so the manufacturers who were serious about offering a credible perimeter system applied various techniques to eliminate nuisance activations.

For the past 18 months, Benchmark has carried out long-term testing on a range of external detectors, and probably the headline result is that nuisance alarms have been extremely minimal for some devices, and non-existent on others. These devices have been out in rain, snow, frost, high winds and heatwaves, and with nothing more than an occasional wipe-over to removed dirt and spiders’ webs, have not created any problem activations. Of course, the lack of false alarms is not the reason to specify an external detector. The most important feature is catch performance. On the occasions when a detector is needed, it is essential that it correctly and accurately reports any intrusions.

During the long-term test Benchmark has worked with external space detection devices from Texecom, Optex and Takex, and all have been in situ for prolonged periods without any issues. Catch performance has been high, with no legitimate alarms being missed.

With regard to external detection, the use of non-overlapping discrete sensing heads, both of which have to detect motion to generate an alarm, has been a game changer. When correctly installed, these devices not only offer a high degree of stability, but also deliver excellent catch performance. They also offer enough flexibility to ensure that a variety of configurations can be deployed.

This approach, when combined with high quality processing, tends to deliver very stable and consistent space detection, without incurring the costs of some of the newer technologies. Indeed, the performance of external detectors in field trials underlines that more often than not the simplest ideas are the best.
During tests, detectors using non-overlapping dual sensor-heads from the established market leaders in the intruder detection field have proven to be the most reliable low-cost options.

One issue with space detectors has always been limited reporting. There is either an alarm or no alarm. However, as the leading manufacturers offer smarter solutions, there is an increased ability to link detectors, set time windows for sequential activations, use AND/OR logic to filter alarms, etc.. This increases the potential on offer from external space detectors and allows bespoke solutions to be easily implemented.

Thermal imaging

Interestingly, at a time when external detection devices were being criticised for their vulnerability to nuisance activations, those offering thermal imaging devices seized on the issues and promoted thermography as a high-end perimeter detection tool. Because of the way in which thermal imagers create image streams, the results lack the level of detail needed for evidential purposes. However, as a detection tool, the technology is well suited to perimeter applications. This is because of the ability of thermography to detect the presence of intruders around the clock, in daylight and darkness, in climatic conditions that would be challenging for mainstream video options. They can also do this over long distances. There is one downside: the cost. Thermal imagers are not cheap.

Just as external detectors improved in terms of performance, so the cost of thermal imagers has reduced with economies of scale. This also coincided with the release of enhanced processors, and many thermal imagers had IVA added, which made them a more attractive proposition for perimeter detection applications.

Thermal imaging resolutions are low, but that has less impact on basic video analytics such as line cross or intruder detection. Indeed, when compared with video-based analytics, thermal imaging has outperformed video for basic detection tasks in Benchmark tests. In many trials, the contrast in thermal imaging might not have been as clear as the differences in video when viewed by a human operator, but the accuracy of the analytics engine was often superior.

Where the real benefits of thermal imaging become apparent is when some form of behavioural filtering is required. While sensors generally tend to alert for any motion in the field of detection, the use of IVA allows a higher degree of flexibility as to which activations create alarms.

For example, alarms might only be required if people cross the perimeter and continue into the site. A ‘first stage’ action, such as switching lights or playing an audio message, might be used for an initial incursion, only generating a full alarm if the intruder then moves into a higher risk area. Staged alarms can also be created using detection devices, but thermal imaging and IVA allows additional behavioural elements to be added.

Discriminations can be set for direction, speed, route followed, dwell time, etc., dependent upon the specific camera being used. It is also possible when using thermal imagers from manufacturers who offer edge-based applications for specific rules-based functionality to be downloaded, thus enhancing the detection performance and criteria.

In bespoke applications, thermal imaging linked with IVA does allow a high degree of flexibility when implementing perimeter-based detection.


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