Car detector   The description about how this is used to detect cars makes no sense Cars are not magnets Moving a magnet near a piece of conductive material will generate a voltage Moving a nonmagnetic piece of steel eg a car near a conductive loop will do nothing Therefore inductive proximity sensors cannot not be purely passive  As I understand their function The proximity detectors in roadsurfaces are actually used as inductor in an oscillator and the proximity of a piece of steel near the loop affects the flow of the magnetic fieldlines from the inductor therefore changing the inductance of the coil Since the coil is used in an oscillator the oscillator frequency then changes which can easily be detected by other electronics  Critically this is very much not a passive system The coils in the roadsurface are constantly emitting a small magnetic field which is what is used to detect the cars presence Also motion of the car is not required or relevant to the sensor detecting the car which is somewhat critical since cars can be stopped at stoplights  Furthermore there seems to be an ongoing conflation of two subjects going on in this article The discussion of the use of inductive coupling to transfer information eg the Discussion of the Telecoil which really should be called a coupled inductor telecoil is just a brandname used apparently exclusively in hearingaids and the use of inductors to detect the presence of objects are very different things and use very different systems Apparently someone has confused the two since they both do use inductors  I will sit down and do some research about the specifics in a few days I need to confirm I understand everything precisely I currently just have a general idea If anyone has any preferences before I rewrite the article a bit please let me know