Motion Sensor Selection

Passive Infrared (PIR), High Frequency (HF) or Microwave, and Ultrasonic motion sensors – which technology to use?

Motion sensors are great tools to manage user behaviour, but selecting the right motion sensor is key to a successful installation.

Here is a quick look at the different types of motion sensor technologies and how they work:

  1. Passive Infrared (PIR): PIR sensors detect the movement of infrared radiation, generated by body heat, between the sensor’s detection bands.
  2. High Frequency (HF): HF (or Microwave) sensors detect movement by sending out a high frequency electromagnetic pulse and measuring the reflection of the pulse – the same principal used by traffic speed guns.
  3. Ultrasonic: Ultrasonic works in a similar fashion to HF motion sensors (sending out ultrasonic pulses), but are becoming obsolete as the HF technology is more reliable and has become more affordable recently.

Comparison of PIR and HF motion sensors:

Passive Infrared (PIR)

High Frequency (HF)/Microwave

PIR sensors rely on changes in temperature to identify movement. These changes in temperature are detected by movement of a heat source (like a human) between the sensor’s detection bands vs HF sensors detect movement by sending out an extremely high frequency electromagnetic signal and checking for changes in the frequency of the signal when it bounces back from objects.
PIR sensors work on ‘line of sight’ and cannot detect temperature changes through solid objects like walls, cubicle dividers or windows. vs HF sensors can detect movement through windows and thin walls,
making them impractical for some office and home applications.
PIR sensors are most effective in detecting movement between detection bands, i.e. movement parallel to the sensor rather than movement towards or away from the sensor. vs HF sensors are most effective in detecting movement towards or away from the sensors.
The closer the movement is to a PIR sensor, the more sensitive the PIR sensor is to smaller movement. vs As long as the movement is in the HF sensor range, the sensor is not much affected by the distance of the object. 


Also see:
Motion Sensor Settings
Motion Sensor Installation
Motion Sensor Best Practices