The eyes have it

Responding to an intruder alarm only to find it is a false alarm is costly, time-consuming and annoying. In 2005 there were more than 368,000 unwarranted alarms in the UK, according to the British Security Industry Federation.

In an attempt to make these a thing of the past, Siemens Building Technologies division has developed the Eyetec system.

It is the first motion detector to combine passive infrared (PIR) with optical detection, rather than traditional motion detectors that use PIR with microwave sensors.

Philipp Angst of Siemens in Switzerland said: ‘Microwave and PIR generate signals that have to be interpreted and only give general information about the incident. Eyetec captures a photo sequence, providing more information on the situation. This gives an unrivalled detection and false alarm rate.’


Sophisticated image processing algorithms track patterns in the motion and evaluate them to determine whether they represent a security threat. In normal operation, Eyetec records images at regular, user-definable intervals that are overwritten when nothing untoward happens. When an event occurs that matches risk conditions, pictures are stored from before, during and after the moment the alarm is triggered.


The sensor’s optical detection system software, operated by a CMOS low-power image chip, employs fuzzy logic to determine an object’s size, speed and direction of travel. It then maps it relative to room position and can even eliminate non-human intruders.


Angst said: ‘The owner of a used car lot in Germany had an office in the middle of the yard with a conventional motion detector that would regularly trip during the night. He installed an Eyetec, which captured pictures of a rat. He was then able to adjust the detector to eliminate anything smaller than human size and was no longer bothered by false alarms.’

The optional IRO Com Tool allows users to set the conditions for triggering an alarm, directly at the detector or at a PC. Combined, the system aims to catch more intruders and prevent unwanted alarms.

The operator can define surveillance zones without making mechanical adjustments to the detector. By marking certain areas on a live image of a monitored room, for example, the user can allow people to enter these zones without triggering the alarm. This would allow museum visitors to walk around valuable exhibits positioned at various points in rooms that are observed by the detector.

The detector can also be set to trigger if it senses people walking in a certain direction. This means that museum staff can monitor if visitors are leaving rather than entering a building at closing time.

As well as heat differences, PIR sensors detect strong light that changes intensity quickly, such as a car headlight or sunlight through blinds. Eyetec uses the Siemens patented black mirror with a special coating to filter out conventional light and only detect infrared.



The anti-blocking feature reports attempts to cover the detector and detects restrictions in its field of view. A back-tampering monitor prevents unauthorised removal of the detector. Any irregularities in its function are also reported.

Angst said one of the biggest challenges was keeping the energy consumption low since in many countries intruder alarm systems are required to have a back-up energy source if the power goes down. Eyetec is designed for low memory and data processing power for image analysis and storage within the detector and is not dependent on a computer.

Another challenge was ensuring Eyetec had the appropriate light sensitivity.

Angst said: ‘It has to work in bright conditions and when getting dark. It also needs to work when dazzled; if there is a bright light source, you still need to see details of the background.’

Eyetec is the first of a new generation of motion detectors. Angst is now working on further improvments.

It is the only motion detector to achieve Grade 4 of EN50131, the highest EU standard for motion detectors.