What temperature change is required to trip a PIR detector?

A passive infrared (PIR) detector is designed to sense changes in infrared radiation, which is primarily emitted by living beings due to their body heat. For a PIR detector to trigger an alarm, it must detect a change in temperature within its sensing range, which typically corresponds to a variation in the infrared radiation level.

The choice indicating 3.6°F is significant because it represents a commonly accepted threshold for PIR detectors, balancing sensitivity and the prevention of false alarms. If the temperature change is around this value, it is typically sufficient for the detector to register movement or heat variation as a signal.

Understanding why this specific threshold is effective involves considering the detector's design and its intended environment. PIR sensors usually have a specified sensitivity level that allows them to respond to body heat effectively while filtering out normal environmental fluctuations. Thus, a temperature change of 3.6°F strikes a practical balance for detecting human movement against the backdrop of varying ambient temperatures.

The other options present different temperature thresholds that may either be too low or too high for standard PIR sensors used in typical applications, thereby either failing to trigger adequately or leading to increased false alarms. Recognizing the specific operational parameters of PIR detectors guides users in deploying these devices effectively in security and surveillance systems.