Jun 05, 2019 · The MQ-2 smoke sensor is sensitive to smoke and also responsive to the following flammable gases: LPG. Butane. Propane. Methane. Alcohol. Hydrogen. The resistance of MQ2 varies depending on the type of gas. The smoke sensor has a built-in potentiometer that adjusts the sensitivity of the sensor based on the accuracy of the gas you are testing.