These board can be used with MQ-2 (Smoke), MQ-3(Ethanol), MQ-4 (Methane), MQ-6, MQ-7/MQ-9(CO and flammable gas) ,MQ-135(Ammonia Gas). The existing board available with the OpenLab is for MQ-3. The sensor measures the ambient air for the presence of alcohol or LPG and produces an analog output. A potentiometer on the module can be varied to change the sensitivity of the MQ-X sensor.