Sensitive material MQ-9 gas sensor is used to clean the air in the lower conductivity of tin dioxide (SnO2). Detection method using low temperature cycling (1.5V heating) to detect carbon monoxide, conductivity sensors with carbon monoxide in the air increased with increasing gas concentration, stray adsorbed at high temperatures (5.0V heating) detection of combustible gases methane, propane and cryogenic cleaning gases. Simple circuit can be used to change the conductivity, concentration of the gas is converted to the corresponding output signal. MQ-9 high gas sensor for carbon monoxide, methane, liquefied petroleum gas sensitivity, the sensor can detect a variety of gases containing carbon monoxide and flammable, is a low-cost sensors for a variety of applications.