Existing Clients: 0208 207 0900
New Enquiries:020 7887 2073
Existing Clients: 0208 207 0900
New Enquiries:020 7887 2073

What is a PIR Sensor and How does it Work?

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What is a PIR Sensor and How does it Work?

The PIR detection technology involved in security systems has changed over the years, with top manufacturers constantly finding new and innovative ways to sense the presence of intruders.

One of the most successful to date is the PIR sensor method found in many of the burglar alarm systems installed in domestic and commercial properties alike. But what is a PIR Sensor? And what makes them so effective?

What is a PIR Sensor?

PIR (passive infrared) sensors utilise the detection of infrared that is radiated from all objects that emit heat. This type of emission is not visible to the human eye, but sensors that operate using infrared wavelengths can detect such activity. They are sometimes referred to as ‘motion-based detectors’, as they sense the presence of people, animals and objects through the movement of their infrared wavelengths.

They are referred to as “passive” due to the fact that no heat or energy is emitted by the sensor itself. It is also important to remember that PIR sensors detect the emission of infrared radiation, and not heat.

How do PIR Sensors Work?

In the case of PIR sensors in burglar alarms, a relay comprises part of a circuit that runs across twin contacts. When the PIR sensor detects motion, it opens the relay, breaking the circuit and triggering the alarm.

At a basic level, PIR sensors operate using positive differential change. Two IR-sensitive slots sit in front of the lens, with their field of “vision” determining the range of detection. While ‘idle’, the ambient level of infrared detected in the room (naturally emitted by all objects) is the same on both slots. The minute an object, person or animal moves through the detecting area, it is sensed by one of the slots before the other, causing a positive differential as it passes by, and a negative differential change as it leaves the area.

These differentials are what the PIR sensor uses to detect movement, sending a message to the alarm panel and sounders if active. It is important to seal the PIR sensor itself inside material that can reduce the outside influences of temperature or humidity, such as metals like silicon.

Pet-Friendly PIR Sensors

PIR sensor-based alarms can be designed to ignore certain shapes of moving objects, or only detect motion above a certain height. This makes them suitable for households that have pets, allowing you to set the alarm before leaving the house in the day without worrying that it will be triggered by your cat or dog moving about.

With over 26 years at the forefront of the industry, AAI Security Systems have become the leading providers of residential and commercial security alarm systems throughout the South East. We design, supply, install and maintain a wide range of high quality burglar alarms and security systems, including pet-friendly units, ensuring that the needs of your property are met. For more information, or to request a survey to assess your requirements, get in touch with AAI today.

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