This is MQ-9 Carbon Monoxide, Methane, and LPG Gas Sensor Module can be used to sense Carbon Monoxide and Methane Gas. Sensitive material of MQ-9 gas sensor is SnO2, which with lower conductivity in clean air.

It makes detection by the method of cycle high and low temperature, and detect CO when the low temperature (heated by 1.5V). The sensor’s conductivity is higher along with the gas concentration rising.When high temperature (heated by 5.0V), it detects Methane, Propane etc. combustible gas and cleans the other gases adsorbed under low temperature.

Features:

High sensitivity to Methane, Propane, and CO
Long life and low cost
Simple drive circuit

Connections :

VCC ➠ Positive pole (5V)
GND ➠ Negative pole
DO ➠ TTL switch signal output
AO ➠ Analog signal output