What is Used to Make Motion Detectors Work?

Motion

• Modern motion detectors actually detect the movement of heat. When a person or animal moves in front of a motion detector, the detector will sense the change in temperature and send a signal to turn on lights or sound an alarm.

Heat

• Heat shows up in the infrared spectrum, which is why motion detectors are sometimes called IR (infrared) detectors. They're also called PIR (passive infrared) detectors because they don't send out a signal to detect motion.

Lens

• Motion detectors have a milky plastic covering that is actually a lens called a Fresnel lens. This is the same type of lens used on lighthouses that focuses and amplifies the energy passing through it.

PIR

• The passive infrared device is a small electronic component behind the lens that senses infrared energy. Heat creates a small voltage change in the PIR sensor, and a separate component measures the change in voltage.

Alarm

• If the voltage change is great enough, a signal is sent to sound an alarm or turn on lights.