Magnetic contacts were the first contactless switching devices. They were known as "axle counting magnets". The iron wheel flanges triggered an actuation by interrupting a magnetic field. The first US patent for an axle counter, filed on 3 June 1960 by Ernst Hofstetter and Kurt Haas, was for a device of this type. During this time, inductive methods were also being produced based on transformers. During the 1970s, developments in the electronics field as well as the introduction of integrated circuits allowed the design of the axle counters currently used.