Most vehicles contain a heated rear window. The heating is performed by an element that is almost invisible when viewed from the drivers seat. Close inspection reveals that there are many small resistance wires embedded within the glass and crossing from one side to the other. When the rear demister switch is turned on, electrical current flows through the wire causing it to heat. This gradually clears a fogged glass allowing the driver to see through it.
Heating elements can also be fitted to exterior mirrors to keep them free of frosting and fogging.
More recent vehicle designs use a similar wire embedded within fixed glass as a radio antenna. The wire is usually separate to the resistance wire and can be located in any fixed window, including the windscreen. Some manufacturers fit the embedded antenna in more than one window.