Electronic smoke detectors, used in furnaces, ovens, etc., for example, in which a beam of light (or infra-red) rays is directed on to a photoelectric cell. According to the density of the smoke, the passage of this beam through the smoke causes variations in the current in the photoelectric cell circuit, thus operating a graduated indicator or a recording system and, in certain cases, a regulating valve. These apparatus may be fitted with an alarm device.
Electronic smoke detectors equipped solely with an alarm fall in heading 85.31.