Sensitive material MQ-4 gas sensor is used to clean the air in the lower conductivity of tin dioxide (SnO2). When there is the environment in which the combustible gas sensor , conductivity sensor with increasing concentration of combustible gases in air increases . Using a simple circuit to convert the change in conductivity of the gas concentration corresponding to the output signal. MQ-4 gas sensor of high sensitivity for methane , propane , butane and has a good sensitivity. This sensor can detect a variety of combustible gases, especially natural gas , is a low-cost sensor for a variety of applications