What does a Passive Infrared (PIR) sensor detect?

A Passive Infrared (PIR) sensor is specifically designed to detect infrared radiation, which is a type of electromagnetic radiation emitted by all objects with a temperature above absolute zero. These sensors are commonly used in motion detection applications, such as security systems and automatic lighting controls, as they can effectively sense the body heat of people or animals moving within their range.

The strength of a PIR sensor lies in its ability to sense changes in infrared radiation levels caused by the movement of warm objects, such as human bodies, against a cooler background. Unlike other types of sensors, PIR sensors do not emit their own signals but rather rely on the changes in infrared radiation in their environment to detect motion. This makes them highly efficient and reliable for lower power consumption and maintaining privacy, as they do not capture images or sounds.

In contrast, the other options relate to different types of sensors: light changes pertain to photodetectors, sound waves are detected by microphones or acoustic sensors, and magnetic fields are monitored by magnetic field sensors. Each of these operates on different principles and is intended for specific applications unrelated to the function of PIR sensors.