PIR vs Microwave Sensors

There are many motion sensors on the market with the most popular being PIR and Microwave sensors. Some offices and gardens may use one of these sensors.

In this article we will explain the difference between the two on how they work, what they do and the best places for the sensor to work.

PIR (Passive InfraRed)

A motion detector that uses PIR technology analyses its environment and looks for a change in present heat signatures. The detector will conduct a room analysis to detect any present heat signatures from the room, it will then revert to its normal state. The motion detector’s trigger will go off when a person enters the detector’s field of view because of the change in heat signatures.

PIR presence detectors detect body heat and movement and are ideally suited to smaller spaces or where a defined detection pattern is required such as: Offices, Boardrooms and Bathrooms/Toilets

Microwave Sensor (MWS)

A microwave motion detector uses microwave technology to analyse its environment. This is achieved by sending out microwave signals, and the length of time it takes for the signal to return to the motion detector is measured. This is known as ‘echo time’. Echo time is the calculation of distances from any stationary object within the detection zone and establishes a baseline for the motion detector to work from.  A motion detector will use a baseline room analysis to detect is current distance from stationary objects within it’s detection range, after which it will return back to a ‘normal’ state. When a person enters the detection zone, this will interrupt the microwave signal and therefore will alter the echo time received by the motion detector. This will be perceived by the motion detector as a change in distance from a stationary object and will therefore cause the motion detector to trigger the alarm.

Microwave presence detectors are sensitive to movement and are ideal for large spaces and areas that have an awkward shape or where fine motion detection is required. They have a much greater coverage and higher sensitivity and can detect movement through glass.

PIR vs. Microwave

PIR detectors can detect the movement of body heat, and are ideally suited where a defined detection pattern is required, such as down a walkway. However they require movement across the infrared beams, meaning they must be installed in the right position to provide effective coverage and can be easily fooled by an intruder.

Microwave sensors are ideal for large spaces and areas that have an awkward shape or where fine motion is detected, such as a garden or driveway due to it providing greater coverage and security. A microwave sensor will offer additional levels of detection that a PIR cannot, such as a pet in the garden or a car pulling into a driveway. These detectors sense motion in terms of speed and size, as opposed to a PIR sensor which senses in terms of heat and light. Microwave sensors can false trigger due to things such as trees blowing in the wind. Although at a reduced sensitivity level, they can also see through plastic, glass and thin walls.

Most PIR sensors affected by the climate, mostly high temperatures and are only rated to IP44. It is often recommended that floodlights with a PIR are installed under eaves to limit the level of water reaching the PIR. Microwave sensors also offer a more stable performance and will operate in temperatures as low as -20°C and as high as 45°C. Microwave sensors offer a longer life span compared to PIR sensors and can still be functioning correctly after 100,000 hours.