This nonautomatic detector has the appearance of a mine official's electric hand lamp. It indicates on an illuminated scale percentages of methane from 0 to 3 in steps of 0.1. When a test for combustible gases is to be made, the projecting front piece is turned part of a revolution; this extinguishes the main light and lights up the illuminated scale. A sample of air is flushed into the detector by means of a small aspirator (or hand pump), the button switch at the side is operated, and the percentage of combustible gases, if any, is indicated on the illuminated scale.