Six Types of Occupancy Sensors Explained

motion sensor on a wall

Electronic occupancy sensors have several uses, including improving home and office security and helping reduce energy use, especially lighting, in unoccupied spaces. Occupancy sensors generally combine a motion detector with a timer and electronic light switch to turn on and off lights when they are not needed. For security, they can be linked to an alarm. Learn more about the six types of occupancy sensors described below.

Types of Occupancy Sensors

Three types of motion detectors: passive infrared (PIR), ultrasonic emitters and microwave emitters, are combined with various devices to make the six types of occupancy sensors.

1. Passive Infrared (PIR) Detector

PIR detectors, the simplest type, have a sensor face that measures different air temperatures in a room. PIR detectors are considered passive because they do not emit any light, sound or heat. Computerized sensors inside the detector compare the average room temperature with the increase in heat that occurs when a human walks past the sensor. The PIR detector sends a signal to switch on lights when a person is in the room. Once the room temperature returns to its average value, a signal goes to the light controls to turn the lights off.

2. Combined PIR and Ultrasonic Detector

motion sensor

A second type of PIR detector is coupled to an active ultrasonic wave-emitting detector. These provide more accurate readings of when people come into and out of a room, enabling more precise control of the lighting system. These are also excellent for use in home security as they can pinpoint the movement of intruders in the home with great accuracy, and activate alarms when needed.

3. Active Ultrasonic Detector

An active ultrasonic detector emits sound waves at levels far above what human ears can hear. The sensors inside the detector receive reflections of these sound waves, indicating the presence of people moving in its detection zone. It can then activate lighting, heat or air conditioning fans, or it can sound an alarm to register an intruder. This advanced technology makes the active ultrasonic detector the most expensive of the six occupancy sensor types.

4. Passive Ultrasonic Detector

A passive ultrasonic detector listens for a range of sound frequencies, usually within 30 feet of its microphone receivers, that alert the detector's sensors to movement. The sensors can then turn on lights or sound alarms as set up in the occupancy sensing or security system. Less expensive than active ultrasonic detectors, the passive detectors are, however, more likely to produce false alarms.

5. Microwave Detector and Occupancy Sensor

Motion sensor light

Microwave-based detectors make the most reliable occupancy sensors at a reasonable cost. Microwaves emitted from the detector cover a wide range to detect movement and activate lighting controls or an alarm. Battery-operated microwave occupancy sensors will work during power outages, so they are ideal for home security.

6. Combined PIR and Microwave Occupancy Sensor

This type of occupancy sensor works well in spaces with windows. PIR detectors cannot detect movement beyond the windows, because glass blocks infrared radiation, but microwave emitters can. This sensor can activate an alarm or turn on interior lights when people approach home or office windows at night.