The gas sensing material used in the MQ137 ammonia gas sensor is tin dioxide (SnO2), which has a low conductivity in clean air. When there is ammonia gas in the environment where the sensor is located, the conductivity of the sensor increases with the increase of the ammonia gas concentration in the air. The change in conductivity can be converted into an output signal corresponding to the gas concentration using a simple circuit.

The MQ137 ammonia gas sensor has high sensitivity to ammonia gas, and is also ideal for monitoring other organic amines (such as trimethylamine, ethanolamine, etc.). This sensor can detect a variety of ammonia-containing gases and is a low-cost sensor suitable for a variety of applications.