Which technology is not used by occupancy sensors to detect the presence of people within a space?

Which technology is not used by occupancy sensors to detect the presence of people within a space?

• A. Ultraviolet
• B. Infrared
• C. Ultrasonic
• D. Microwave

Answer: (A)

Detecting occupancy relies on signals tied to people inside a space—heat, movement, or changes in distance. Ultraviolet light isn’t used for this purpose because humans emit most of their body heat in the infrared range, not in the ultraviolet. Using UV would require emitting UV radiation and exposing occupants to it, which is unsafe and unnecessary for sensing presence. Infrared sensing detects the heat signatures from people as they move, triggering the sensor when there’s a noticeable change. Ultrasonic sensing uses high-frequency sound waves; as people move, the reflections of those waves change in a way the device can detect, signaling presence. Microwave sensing sends microwave radio waves and monitors reflections and Doppler shifts to detect movement, even through some barriers like furniture or lightweight partitions. So the technology not used for occupancy detection is ultraviolet.

Detecting occupancy relies on signals tied to people inside a space—heat, movement, or changes in distance. Ultraviolet light isn’t used for this purpose because humans emit most of their body heat in the infrared range, not in the ultraviolet. Using UV would require emitting UV radiation and exposing occupants to it, which is unsafe and unnecessary for sensing presence.

Infrared sensing detects the heat signatures from people as they move, triggering the sensor when there’s a noticeable change. Ultrasonic sensing uses high-frequency sound waves; as people move, the reflections of those waves change in a way the device can detect, signaling presence. Microwave sensing sends microwave radio waves and monitors reflections and Doppler shifts to detect movement, even through some barriers like furniture or lightweight partitions.

So the technology not used for occupancy detection is ultraviolet.