This part is a kind of semiconductor called MQ-2.
Function of this product has Semiconductor Sensor for Combustible Gas.
Manufacturers : ETC
Image and pinout :
Some of the text within the PDF file :
MQ-2 Semiconductor Sensor for Combustible Gas Sensitive material of MQ-2 gas sensor is SnO2, which with lower conductivity in clean air. When the target combustible gas exist, The sensor’s conductivity is more higher along with the gas concentration rising. Please use simple electrocircuit, Convert change of conductivity to correspond output signal of gas concentration. MQ-2 gas sensor has high sensitity to LPG, Propane and Hydrogen, also could be used to Methane and other combustible steam, it is with low cost and suitable for different application. Character *Good sensitivity to Combustible gas in wide range * High sensitivity to LPG, Propane and Hydrogen * Long life and low cost * Simple drive circuit Configuration Application * Domestic gas leakage detector * Industrial Combustib [ ... ]