This is an Arduino CO/Combustible Gas sensor. It uses MQ-9 to dectect Carbon Monoxide. The sensor can be used to detect different gases containing CO and combustible gases, it is low cost and suitable for a variety of applications.
The core sensing material of MQ-9 gas sensor is SnO2, which has a lower conductivity in clean air. It makes detection by cycling high and low temperature, and detects CO when low temperature (heated by 1.5V). The sensors conductivity is higher along with the gas concentration rising. When temperature rises (heated by 5.0V), it detects Methane, Propane, combustible gas,etc and cleans the other gases adsorbed under low temperature.
The sensitivity can be adjusted by the potentiometer. The output is proportional to the density of gas. You can use analog reading to read the data from this sensor.
To ease the difficulty of using this sensor, a Gravity Interface is adapted to allow plug&play. The Arduino IO expansion shield is the best match for this senor connecting to your Arduino microcontroller.