Occupancy Sensors

What are they?

Occupancy sensors detect people moving in the building and  can be used to automatically switch lights on and off. Typically, the light will turn off following a set period of inactivity in a space and on again  once activity is detected, usually when someone enters the space.

There are several different types of occupancy sensor, including  passive infrared sensors (PIR) which are the most cost effective but least sensitive, ultrasonic, microphonic and microwave, as well as some sensors that use more than one of these technologies.  The best type of sensor depends on the application.

Advantages / Disadvantages

Energy is saved by the automatic switching off of lighting in unoccupied areas.

A low cost feature, this typically achieves payback in less than 5 years.

Poorly designed or commissioned systems can cause annoyance to occupants due to lights turning off while occupants are still present.

Energy efficiency

Energy is saved by the occupancy sensor switching off the lights after a period of inactivity in a particular area.

Running costs

Occupancy  sensors require periodic checking to ensure they are functioning correctly.  Overall running costs will reduce due to the energy savings achieved.

Retrofit / improvement opportunities

Occupancy sensors can be readily fitted to many existing lighting installations.  Successful retrofit involves careful selection of the appropriate sensor for the job and careful commissioning to ensure that it works properly.

Applicable buildings

Occupancy sensors are suitable for any part of a building that does not have continuous and constant occupancy.

Floor plate implications

Occupancy sensor locations need to selected to match the coverage pattern of the sensor and the configuration of the space being covered.   Sensors will generally need to be repositioned if tall partitions or walls are moved.

Occupant comfort

Frequent switching of lights caused by poor positioning and configuration of occupancy sensors can be frustrating for occupants.  Low use spaces, such as toilets, fire stairs, and storage areas are less likely to cause problems, as long as occupants are not left in the dark

Maintenance implications

Occupancy sensors have low maintenance requirements but need to be kept  clean. The operation of the sensors should be routinely checked.


Sensors mounted high on the wall, in a suspended ceiling or as part of a light fitting.

Questions to ask

  • Are occupancy sensors used in the building, and if so, where?
  • When were the PIR sensors last checked / maintained?

More information

References needed