The MQ 135 Air Quality Detector Sensor Module For Arduino has lower conductivity in clean air. When the target combustible gas exists, the conductivity of the sensor is higher along with the gas concentration rising.
Convert change of conductivity to the corresponding output signal of gas concentration. The MQ135 gas sensor has high sensitivity to Ammonia, Sulphide and Benzene steam, also sensitive to smoke and other harmful gases.
It is with low cost and suitable for different applications such as harmful gases/smoke detection.