Infrared Sensor

Many of these types of sensors only measure infrared radiation, rather than emitting it, and thus are known as passive infrared sensors.

All objects emit some form of thermal radiation, usually in the infrared spectrum. This radiation is invisible to our eyes, but can be detected by an infrared sensor that accepts and interprets it.

In a typical infrared sensor like a motion detector , radiation enters the front and reaches the sensor itself at the center of the device. This part may be composed of more than one individual sensor, each of them being made from pyroelectric materials, whether natural or artificial.

They are wired in such a way so that when the sensor detects an increase in the heat of a small part of its field of view, it will trigger the motion detector's alarm.

It is very common for an infrared sensor to be integrated into motion detectors like those used as part of a residential or commercial security system.

A set of these lenses on a motion detector can focus light from many directions, giving the sensor a view of the whole area.

A sudden change in one area of the field of view, especially one that moves, will change the way electricity goes from the pyroelectric materials through the rest of the circuit. This will trigger the motion detector to activate an alarm.