NFPA 731, Section 5.2 is all about monitoring methods for exterior locations around the protected premises for a security breach. Typical exterior monitoring methods can include photoelectric detectors and motion sensors.

• The photoelectric detector will trigger when a beam of light has been interrupted or crossed.
• The motion sensor senses unauthorized movement.

There are two basic types of motion sensors; passive sensors and active sensors. Passive sensors use infrared technology to detect body heat while active sensors send out ultrasonic sound waves which reflect back to the sensor. The sound waves continue until disruption such as a person walking by which can trigger an alarm signal.

Below is a sample of NFPA 731. For the complete section, see the actual NFPA 731 text at NFPA.ORG. Once there, click on the free access link to the latest edition of NFPA 731.

5.2 Exterior Space Detection Systems. Signals from exterior space detection systems shall not be dispatched as an alarm unless alarm verification in accordance with 9.6.1.1 is used.

5.2.1 Photoelectric Detector.

5.2.1.1 Photoelectric detector units shall be in compliance with applicable standards, such as ANSI/UL 639, Standard for Safety for Intrusion-Detection Units.

5.2.1.2 An alarm signal shall be initiated when a minimum of two of the following parallel units mounted on the same vertical plane are activated:

(1) Two photoelectric detector units

(2) One photoelectric detector unit and one unit of another technology as described in this standard

5.2.2 Motion Detection.

5.2.2.1 Motion detection units shall be in compliance with applicable standards, such as ANSI/UL 639, Standard for Safety for Intrusion-Detection Units.

5.2.2.2 Passive infrared (PIR) units shall meet the requirements of ANSI/SIA PIR-01, Passive Infrared Motion Detector Standard — Features for Enhancing False Alarm Immunity.