Q. When gas leaks, why does a gas sensor buzz?

A. I will explain the type of sensor in which a ceramic made with the white powder of tin oxide or a semiconductor detect gas. The tin oxide is a n-type semiconductor and since it has many electrons that can move freely, oxygen in the air combines with it. When oxygen combines, it becomes an ionic form of oxygen (oxide ion) by taking the electrons that tin oxide has. This is the most common situation. If the gas (propane gas and methane gas in city gas) comes there, the gas takes the oxygen that combines with tin oxide away. When the oxygen separates from tin oxide, it leaves the electrons that it gained. Therefore, the number of electrons increases and they flow. Since the flow of electrons means a flow of electric current, this electric current makes a buzz and noise. By the way, since there is no smell to the gas used at home, a gas that smells strange is intentionally mixed.