Passive infrared (PIR) sensors detect intruders by identifying differences in infrared radiation, which is emitted as heat. Every object emits infrared radiation based on its temperature. When an intruder passes through a PIR sensor’s field of view, their body heat contrasts with the background temperature, causing the sensor to trigger an alert.

PIR sensors are commonly used in security systems due to their reliability in detecting human movement while minimizing false alarms. They are highly effective in environments where the ambient temperature is relatively stable, enabling clear differentiation between the human body and the surroundings. PIR sensors are optimized for detecting the movement of warm objects, such as a person walking, against the cooler background.

This mechanism works using a pyroelectric sensor that is sensitive to infrared radiation changes. As an intruder moves within the sensor’s detection zone, the temperature variation is registered and processed, resulting in an activation signal.

Key Advantages of PIR Sensors in Security Systems:

Energy Efficiency: Passive sensors do not emit energy; they detect existing infrared radiation, making them energy-efficient.

Reliability: Reduced false alarms compared to other motion detection technologies, especially in stable thermal environments.

Cost-Effective: PIR sensors are widely available and affordable, making them a popular choice for residential and commercial security applications.

ASIS Certified Protection Professional (CPP®) References:

Physical Security Principles: Understanding the mechanisms of detection technologies is critical for selecting appropriate systems for a security plan. PIR sensors are classified under thermal detection systems due to their reliance on infrared radiation.

Technology Integration: PIR sensors are often integrated into broader physical and electronic security systems, as discussed in ASIS CPP materials on layered security approaches.

False Alarm Reduction: CPP materials highlight the importance of matching sensor technology to the environment to reduce false positives, a feature where PIR sensors excel when applied correctly.

For additional validation, refer to ASIS Physical Security Applications Module and CPP Review Manual, Chapter 4: Detection Systems.