Intruder photoelectric units shall be mounted at what height?

• A. 6 to 12 inches
• B. 60 to 72 inches
• C. Not less than 18 inches nor more than 36 inches
• D. 12 to 18 inches

Answer: (C)

Key idea: where you place an intrusion photoelectric unit affects how reliably it detects a person while avoiding false alarms and tampering.

Mounting it between 18 and 36 inches from the floor places the sensing element in the zone where a person walking or passing through a doorway is likely to interrupt the beam or trigger the detector. This height avoids common nuisance triggers from low-lying objects, dust, or pets that occur when the device is mounted too low, and it isn’t so high that an average intruder can bypass the sensing path or that the beam isn’t intercepted effectively. It also keeps the unit out of easy reach for tampering while still being accessible for maintenance. For these reasons, the recommended range is not less than 18 inches and not more than 36 inches.