The sensor consists of a porous core of some magnetic material with an induction coil wrapped around it. Exposure of th core to oxidizing or reducing gases causes chemical changes to occur. These result in changes in the core’s magnetic properties which are observed as changes in the inductance of the coil. Measurements of the time rate of change of the inductance are used to determine the concentration of the active species in the gas stream. Among the materials which have been used to demonstrate these principles are magnetite to detect O2 or other oxidizing gases and α‐Fe2O3 for CO, H2 and other reducing gases.One advantage of the magnetic gas sensor over other solid‐state gas sensors is the fact that the coil can be separated physically from the core and gas stream by an insulating coil form, making it feasible to use this device at elevated temperatures and in corrosive environments.