Sensitive material of MQ-6 gas sensor is SnO2, which with lower conductivity in clean air. When the target flammable gas exist, the sensor’s conductivity gets higher along with the gas concentration rising. Users can convert the change of conductivity to correspond output signal of gas concentration through a simple circuit. MQ-6 gas sensor can detect kinds of flammable gases, especially has high sensitivity to LPG (propane). It is a kind of low–cost sensor for many applications.