What characterizes a passive sensor like a PIR?

A passive sensor is characterized specifically by its ability to detect changes in environmental conditions rather than generating its own signals. In the case of a Passive Infrared (PIR) sensor, it is designed to respond to the infrared radiation emitted by objects within its field of view, particularly warm bodies like humans and animals. This means that the sensor operates by sensing the infrared energy that is naturally present in the environment, which is a hallmark of passive sensors.

The mechanism of detecting changes in infrared radiation allows PIR sensors to identify motion and presence. This ability is crucial for applications like security systems, where the detection of movement can trigger an alert.

Understanding this characteristic helps in differentiating between types of sensors. For instance, active sensors would emit their own signals and analyze the reflected energy to detect objects, while passive sensors like the PIR rely solely on external energy sources—in this case, naturally occurring infrared radiation.