The crowtail- Gas Sensor(MQ9) module is useful for gas leakage detection (in home and industry). It is suitable for detecting LPG, CO, CH4. Due to its high sensitivity and fast response time, measurements can be taken as soon as possible. The sensitivity of the sensor can be adjusted by using the potentiometer.There are different gas detectors for sale, like MQ2, MQ3 and MQ5. Below is a contrast table of them.