The GJC4(A) low-concentration methane sensor for mines is developed to meet the needs for methane concentration monitoring of coal mines in China. It is capable of continuously and automatically converting the underground methane concentration into standard electrical signals and transmitting them to the associated equipment. It has the functions of local display of methane concentration, over-limit sound and light alarm, etc. This sensor has been subject to online inspection by the national explosion-proof test agency. It can be used with monitoring systems, power-off devices and air, electricity and gas blocking devices at home. It is applicable to fixing on mining faces, mechanical and electrical equipment chambers and ventilation roadways in coal mines.