The MQ2 sensor is one of the most popular sensors in the MQ family. It is a type of MOS (Metal Oxide Semiconductor) sensor. These kinds of sensors are also called chemiresistors because they work by changing their electrical resistance when they come into contact with certain gases.
 
The MQ2 gas sensor runs on 5 volts of DC power and uses about 800 milliwatts of energy. It can detect several types of gases, including LPG (liquefied petroleum gas), smoke, alcohol, propane, hydrogen, methane, and carbon monoxide. This sensor can detect these gases when their concentrations are between 200 and 10,000 parts per million (ppm).
 
 
Features
Operating Voltage is +5V
Can be used to Measure or detect LPG, Alcohol, Propane, Hydrogen, CO and even methane
Analog output voltage: 0V to 5V
Digital Output Voltage: 0V or 5V (TTL Logic)
Preheat duration 20 seconds
Can be used as a Digital or analog sensor
The Sensitivity of Digital pin can be varied using the potentiometer