Which of the following can be a source of false alarms for PIRs?

The correct answer is bright white lights because they can trigger passive infrared sensors (PIRs) by causing a sudden change in the thermal environment. PIR sensors detect variations in infrared radiation emitted from objects in their field of view. They are designed to sense changes in heat signatures, such as the movement of a warm body, like a human. However, bright white lights can create significant heat, or they may mask the thermal signature of a person moving through the sensor’s area, leading to incorrect readings and false alarms.

In contrast, excessive noise does not directly influence the infrared detection capabilities of a PIR. Low temperatures generally do not trigger false alarms unless they cause significant changes in the detection area, such as frost on the sensor's lens. Limited visibility might limit the sensor's effectiveness, but it does not inherently create false alarms like the presence of bright lights can, which directly affects the thermal backdrop the sensor is expecting to interpret.