MQ-2 gas sensor module has high sensitive to LPG, Propane and Hydrogen, also could be used to Methane and other combustible steam, it is with low cost and suitable for different application. Working Gas: Carbon Monoxide, LPG, Alcohol/ Ethanol, Propane, Hydrogen, Methane, and Butane Working voltage: DC 5V, DOUT: TTL output, AOUT: Analog output, Preheat time: Over 20s.