Which of the following could cause a PIR motion detector to give a false alarm?

• A. Heat/air currents
• B. Sunlight
• C. Loose screws
• D. All of the above

Answer: (D)

PIR sensors detect changes in infrared energy in their field of view, so a false alarm happens whenever something changes the IR pattern without an actual intruder.

Heat and air currents can move warm air across the sensor or create shifting heat patterns, making the detector think something moved. Sunlight can produce sudden IR changes as it sweeps across the sensor or reflects off surfaces, triggering a alarm even though no one is present. Loose screws or a loosely mounted unit can allow the sensor to shift or vibrate, altering its viewing angle or sensitivity and causing false triggers.

Since each of these scenarios can cause a false alarm, the best answer is all of the above. Keeping the sensor away from heat sources and drafts, shielding it from direct sunlight, and securing the mount helps reduce false alarms.