`  == 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 non-magnetic piece of steel (e.g. 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 road-surfaces 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 field-lines 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 road-surface are constantly emitting a small magnetic field, which is what is used to detect the car's 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 stop-lights.  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 (e.g. the Discussion of the ``Telecoil``, which really should be called a coupled inductor, telecoil is just a brand-name used apparently exclusively in hearing-aids), 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 re-write the article a bit, please let me know.   `