Assessment: Intrusion Detector Stability

The world of intruder detection never stands still. Professional manufacturers work tirelessly to enhance the catch performance of sensors and improve overall levels of accuracy. Unfortunately, too many people still think about detectors solely in terms of false alarm immunity, which can serve to undermine the progress that has been made in regards to improved detection capabilities. Given how common the use of detectors is in security applications, some practices are still based on the performance of decades ago!

In a technology-based arena such as the electronic security industry, nothing stands still for long. Some changes make headlines and attract all of the interest, but this does not mean that the big news stories are all that is happening. Often the small incremental developments go unreported and over a period of time that can mean significant improvements in performance. It is only by standing back and considering how devices performed five or ten years ago that you see just how far things have advanced.

The world of intruder detection is arguably the longest established part of the security industry. Back when access control largely consisted of higher grade keys and locks and video surveillance offered low quality time-lapsed footage to those with very deep pockets, intruder alarm systems dominated the market.

It is fair to say that in its early days, intruder detection had some issues with regard to false alarms. With the introduction of the ACPO security systems policy in the 1990s, the focus on false alarms was swiftly brought into focus. Of course, the term ‘false alarm’ is something of a misnomer; typically such events did have a cause. The issue was that the cause often wasn’t what the installer and user expected it to be.

False alarms were generally a wide range of incidents that were conveniently lumped together to simplify the arguments being presented by ACPO. For example, if an end user saw a crime being committed and used a panic alarm to summon the police as it was the quickest way, that was logged as a false alarm. This was in an age when the police service advertised that it needed people to report anything suspicious; the ‘keep them peeled’ years. Admittedly, it was never envisaged that the public would use PAs to summon the police to on-going crimes, but to tag incidents like this, along with general user error, as false alarms did little to reflect the true stability of intruder detection systems.

Other issues such as environmental conditions also impacted on systems, as did the installation of devices in areas which would prove to be troublesome. Whilst such events (along with user-generated problems) were classed as false alarms in that they were not confirmed activations due to intrusion that were passed to the police, they did serve to give a incorrect impression that intruder alarm systems were generally unstable.

One downside of this was that detectors seemed to bear the brunt of complaints about instability. At the time there wasn’t any significant research that showed detectors to be the weak link in the system, nor were they any technological issues that were indicative of a need for greater care when selecting sensors.

However, with the spotlight on detector performance, manufacturers became quite vocal about how the designs of their products reduced false alarms. This in itself arguably did more to cement an idea in many people’s minds that detectors could be unstable and unreliable and the sales message was more about detectors that wouldn’t generate false alarms than ones that would quickly and accurately detect genuine intrusions.

Interestingly, when the team at Benchmark tested detectors – both PIRs and dual technology devices – during that period we had very few issues with regard to nuisance activations. On the few occasions that we did experience problems they were usually issues relating to over-sensitivity which could either be adjusted out or solved by taking a different approach to the sensor location.

Despite the wide range of detectors available generally giveing high levels of accurate performance, the negative thinking about false alarms led to significant changes, not least the need for ‘confirmed activations’.

Dual stability?

Intruder detection devices fell into two main camps comprising internal and external units. In the past external detection devices were frowned upon. They could not be included in graded alarm systems and many saw their usefulness as limited to switching lighting. With regard to internal units, the main ‘flavours’ were PIRs and dual technology detectors. The latter typically comprise a mix of PIR and microwave technologies.

As a rule of thumb, most internal applications made use of PIRs. In typical conditions the detectors worked well and had very effective catch performance. However, for applications where environmental conditions were challenging, dual technology detectors offered a different solution.

Dual tech devices are ideal for applications where there is a higher risk of background infrared activity to a degree that a standard PIR might be impacted. Dual tech units are generally larger and more costly than PIRs (as they include a PIR plus a microwave sensor).

Installers and integrators would subsequently limit the use of dual technology devices to challenging environments such as those where hot and cold air blasts were present of where animal activity could not be prevented.

Unfortunately, there was also a common workaround where if a PIR was causing issues, usually due to be sited in a position where nuisance alarms were being generated, it would be exchanged for a dual tech device rather than relocating the original PIR. As stated, this was a common approach with some installers and integrators but wasn’t a best practice use of the technology.

If a nuisance event was causing a PIR to trigger, the best approach is to assess the case and either remove it or relocate the PIR so it still offers coverage of the area without being affected. Simply replacing it with a dual technology detector means that the risk of the PIR element being impacted still remains. As such, the area is being protected by a single microwave element, because the PIR element could be compromised at any given time.

The use of dual technology detectors was further increased when ACPO insisted that alarm activations needed to be confirmed, in that two separate detector activations needed to be signalled for an alarm event to be policed. To achieve this it was decided that two detectors of the same technology could be used so long as the fields of detection did not overlap, or two detectors of differing technologies could be used with overlapping fields of view permitted. In effect, this meant that a single technology PIR could be used with an overlapping dual technology detector to create a confirmed event, despite overlapping detection fields having been considered not best practice for many years.

The outcome was that the dual technology detector was no longer viewed as a device for specific applications and environments. It also created the impression that detectors were not stable or reliable.

Today’s sensors

Modern detection devices, both indoor and outdoor sensors, have evolved significantly in recent years. Also, PIRs have developed with regard to all elements of operation. Catch performance has improved, as has accuracy and discriminations that allow nuisance sources of IR activity to be ignored. Stability has also improved.

Because many of the developments have been incremental, this means those using detection devices won’t have experienced a significant and noticeable change. However, the increase in performance is obvious when detectors from differing generations of product are tested in hostile environments side by side.

There is still a place for dual technology detectors. In certain applications they remain the best choice for both catch performance and stability and their use is necessary where environments are hostile or prone to conditions that might interfere with an infrared sensing device. In both internal and external situations, dual technology detectors have their uses. However, this should not include being used as a workaround for poorly sited PIRs, nor should it be assumed that dual technology detectors offer more stable performance than single technology devices.

The electronic security industry is currently benefitting from advances in processing capabilities. The video surveillance and access control markets are using the additional processing power in some very interesting ways.

Many of the advances this enables – advanced smart video analytics, deep learning and AI, additional edge-based services, value added functionalities – are big news in the relevant sectors.

This is because the changes allow implementations that were not previously possible. However, whilst detection devices are able to leverage chipsets with greater processing capabilities, the majority of the benefits enhance performance rather than adding additional headline-grabbing functions. This means that the signal processing capabilities are improved, enabling higher degrees of accuracy. Because of this, detectors are better able to assess infrared signatures and thus deliver significant results.

As well as advanced processing, modern detection devices benefit from high quality optics. Economies of scale also mean that an increased number of PIR detectors for external applications make use of mirror optics. Whilst not a new technology, mirror optics have decreased in cost and so sensors that make use of them have become a more realistic option for many applications.

Mirrored optics can deliver more accurate detection as the plates can be manufactured to high tolerances which gives more precise focussing. This also allows the full potential of advanced processing to be realised.

Another change in the design of detectors has been the greater use of dual or even triple sensors with non-overlapping views in external units. This enables the installer or integrator to mount a device in such a manner that innocuous motion, such as small animals or wind-blown debris, does not trigger alarms. By arranging the detection fields it is possible to ensure that only targets of a human size are detected.

This has the effect of creating a ‘double knock’ scenario using a single detector and the lack of overlapping coverage further ensures a higher degree of accurate catch performance.

Many of the advances are shared across internal and external devices for both single and dual technology detectors. For the installer and integrator, this means that whilst the world of intruder detection hasn’t enjoyed many headline-grabbing changes, the performance of sensors has continually been improved.

Benchmark has tested many current detectors on a site that is also fitted with older professional grade sensors. While the latter products do not create problems, in extreme conditions or when pushed in terms of performance, the new models are significantly better at delivering appropriate detections.

In summary

It is important that installers and integrators select the right detection devices, in terms of technology and build quality. If credible manufacturers with an established track record in detection are selected, the products will be based upon tried and tested components and designs.

It is also important that those designing security installations select the right technologies. Dual technology detectors have their place, and when required due to hostile environments nothing else should be specified. However, the devices should not be considered solely as a ‘quick fix’ where problems arise.

If a professional detection device is specified and is giving problems, the issue is more likely to be with the location of the sensor rather than the detector itself.

Finally, it is worth remembering that motion sensing will increasingly be deployed for automation and management applications. Smart systems rely upon triggers and inputs to deliver appropriate actions, and as a result the industry will see cheaper detectors arriving from IoT and smart home manufacturers. Given the advanced engineering built into professional security sensors, best practice is always to use a proven security sensor.

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