Abstract: An infrared detector of sufficient sensitivity and stability to provide for the reliable detection of a glowing ember moving through an enclosed carrier system (duct or conveyor) in which a photo-resistive device for viewing the interior of the carrier is connected into suitable circuitry that does not respond to slowly changing ambient light, but which produces a voltage pulse in response to a moving glowing ember passing through the field of view of the detector; said voltage pulse being utilized to provide an output signal which may actuate an alarm or release extinguishant.