Methane gas Sensor - MQ-4 (analog and digital out).
This semiconductor gas sensor detects the presence of methane (CNG) gas at concentrations from 300 ppm to 10,000 ppm, a range suitable for detecting gas leaks. The sensor’s simple analog voltage interface requires only one analog input pin from your microcontroller.
There are two modifications of the sensor:
Standard - with sensitivity.
With analog and digital outputs - with the amplifier output signal and adjusting the heating element sensor. You can configure the sensor to a certain threshold, and connect to the digital input of the microcontroller.