This is an Arduino CH4 gas sensor. It uses MQ4 probe which is able to detect natural gas, CH4. It is less sensitivity in detecting alcohol, cooking fumes, and cigarette smoke.

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.

Improvement List:

Standard assembling structure (Times-of-5mm Center distance between two 3mm(0.12") mounting holes)
Easily recognitive interfaces of sensors ("A" for analog and "D" for digital)
Icons to simplely illustrate sensor function
High quality connector
Immersion gold surface