This is a very easy to use low cost semiconductor Gas sensor Module with analog and digital output. This module uses MQ2 Smoke & Flammable gas sensor as a gas sensing element. It requires no external components just plug in Vcc & ground pins and you are ready to go. For Digital output the threshold value can be easily set by an on-board potentiometer.  Using this module you can easily interface MQ2 Smoke & Combustible gas Sensor to any Microcontroller, Arduino or even Raspberry Pi. Since this Gas Sensor module is sensitive to smoke it can be used in for fire detection. MQ2 Gas Sensor is also sensitive to flammable/combustible gasses like LPG, Propane & Hydrogen.