The crowtail - Gas Sensor(MQ2) module is useful for gas leakage detecting(in home and industry). It can detect LPG, i-butane, methane, alcohol, Hydrogen, smoke and so on. Based on its fast response time. measurements can be taken as soon as possible. Also the sensitivity can be adjusted by the potentiometer.There are different gas detectors for sale, like MQ3, MQ5 and MQ9. Below is a contrast table of them.