Sensitive material MQ-4 gas sensors used in clean air, low conductivity tin oxide (SnO2). When there is an environment in which the combustible gas sensor, conductivity sensor with increasing concentration of combustible gases in air increases. Use simple circuit can convert the change in conductivity of the gas concentration corresponding to the output signal. MQ-4 Methane gas sensor of high sensitivity, pane, butane and has a good sensitivity. The sensor can detect a variety of combustible gases, it is a low-cost sensor suitable for a variety of applications.