Which type of sensor is categorized as active in security systems?

The photo beam sensor is categorized as an active sensor in security systems because it emits a signal, often in the form of a light beam, and detects interruptions in that signal. When an object passes through the beam, it disrupts the transmission, which triggers an alarm or alert. This active mode of operation, where the sensor itself generates a signal to monitor its environment, differentiates it from passive sensors, which only detect changes in the environment without emitting their own signals.

In contrast, passive infrared sensors detect heat emitted from objects, such as people or animals, but do not send out a signal themselves, making them passive. Reed switches and magnetic contact sensors rely on a magnetic field and mechanical operation to function, which means they also do not emit a signal. These distinctions help clarify the operational dynamics of different sensor types in security systems.