ESA Certified Alarm Technician Practice Exam

Passive sensors are characterized by their reliance on environmental changes to detect and respond to stimuli. Unlike active sensors, which emit their own signals (such as infrared or ultrasonic waves) and measure the reflections of those signals to determine the presence of an object or condition, passive sensors simply detect existing energy in the environment. For example, a passive infrared sensor picks up heat emitted from a person or object without sending out its own signal.

Because passive sensors only need to respond to changes in the environment, they often require less maintenance and are generally simpler in design than active sensors, which must continuously generate signals and analyze return data. This fundamental operational difference distinctly defines how these types of sensors function within alarm systems and other applications.