Which items can cause a false alarm on a motion sensor?

• A. Pets, Mylar balloons, Fax machines, heater vents
• B. Rain, puddles, wind
• C. Ground vibrations, HVAC noise
• D. Sunlight glare through windows

Answer: (A)

Motion sensors, especially passive infrared ones, respond to changes in infrared energy in their field of view. Any moving heat source or rapid change in the thermal pattern can trigger a false alarm, even if there’s no intruder.

Pets are a common source because they move around and create new heat signatures as they wander through the area. Mylar balloons can drift with air currents, causing shifting reflections or alterations in the heat pattern that the sensor interprets as motion. A fax machine or similar device nearby produces localized heat and may have moving internal parts; that temporary change in heat within the sensing zone can set off the detector. Heater vents push warm air into the space and create moving warm plumes, which the sensor can read as movement.

Other factors like rain, puddles, wind, or sunlight glare can affect some sensors, but the combination of moving pets, drifting reflective objects like balloons, nearby heat sources from office equipment, and warm air from vents are classic indoor false alarm culprits for motion detectors.