What is the function of the PIR (Passive infrared) detector?

• A. Function- motion/inferred sensors
• B. Function- door contact
• C. Function- power supply
• D. Function- tamper detection

Answer: (A)

PIR detectors sense motion by monitoring changes in infrared energy within their view. They use a pyroelectric sensor to detect differences in heat energy between adjacent zones, so when a warm body moves across the field of view, the sensor outputs a signal that the alarm system interprets as presence or motion. Because they’re passive, they don’t emit any energy themselves—they only detect what’s already in the environment. That’s why their function is best described as motion or inferred presence sensors. The other terms describe different components: a door contact detects opening/closing, a power supply provides electrical power, and tamper detection flags if the device is being interfered with.