Which of the following is an unusual cause of a false alarm?

• A. Car headlights at night coming through windows or curtains or bouncing off mirrors
• B. A squeaky door hinge
• C. Dust on the sensor
• D. A power outage during the night

Answer: (A)

False alarms happen when a detector interprets something as an intrusion even though there isn’t one. An unusual cause is something external and not a typical sensor fault, like car headlights at night shining through windows or reflecting off surfaces. Those lights can momentarily alter what a sensor “sees” or feels in its field of view, triggering a false alarm in ways that aren’t part of everyday sensor noise or mechanical issues.

Dust on the sensor is a common offender because it directly affects the sensor’s ability to detect properly. A squeaky door hinge can produce vibrations that trigger a contact sensor when a door moves. A power outage is more about the system losing power and going into a fault or standby state than about producing a false alarm from normal detection. So the headlights through windows stand out as the unusual, external cause.