We do not know who invented this great device if you could shed more light on its development then email us and let us know. 

Being of a only slightly advancing age we can though remember cars without one, and what a complete pain they were. In fact my first car was a seventies mini, which did not have a standard fitted one.  In those days of the early eighties you could still buy a stick on one. It wasn't quite as sophisticated as a factory one , resembling as it did a electric blanket element with bars a half inch thick. At least they were sort of reliable unlike early factory efforts many of you may remember buying small bottles of metallic paint repaint in the little lines when they broke.

Things have moved on from those early days. Today's element are reliable barely visible devices, often protected by a timer, or temperature sensor.  Some of course are multi-function in that they also act as an aerial for the radio. This was developed by GCE in Salford, but the company folded before it could take advantage of the market.     

Fixing a heated rear window

Troubleshoot your problem as follows:
1) Locate the fuse and make sure it's still good. An ohmmeter would read 0 ohms (ohms are represented on the meter as the Greek omega). If the fuse is bad, replace it. If it's good, set the meter to read voltage, touch the black lead to a bare metal chassis ground, and use the red lead to check for voltage at both of the fuse clips. One should have 12 volts. If the voltage is there and the fuse is good and the rear defroster still doesn't work,
go to step 2.

2) Check for power at the rear window. Go back to the rear window and disconnect the wires. Do what you have to do to run the rear defogger. Does the car have to be running? With the rear defroster switched on, measure voltage between the two wires. My guess is that it should read 12-14 volts WHEN DISCONNECTED FROM THE WINDOW. If there's no voltage reading between the wires, measure for voltage from each wire to chassis ground. It's possible that one of the wires going to the window simply supplies a path to chassis ground, and there may be a bad connection to the base unit which keeps the window from working even though the 12v is being supplied to the other connection. If one wire has 12v compared to chassis ground, the other wire must be the ground lead. Turn the power off and use the ohmmeter to measure resistance between the connector and the chassis. It should be a steady reading near zero ohms. If not, find the place where it connects to the chassis and make sure that it is clean and tight. If there's voltage between the two wires and the connectors are sound, the window must be bad.
Go to step 3 to confirm.

3) To see if the window is okay, you'd be better off measuring continuity, i.e., resistance in ohms with the power off. As long as there's no break in the bands in the glass, they have to heat up when voltage is applied and current flows through them. Find the wires that go to the window, disconnect them and measure them with an ohmmeter (multimeter set to resistance). The conductors have built-in resistance since they need it to generate heat as current flows through them, but the number measured on one that is intact should be pretty low. Electric defrosters like this usually stop working due to a break in the conductor in the glass. If the conductor is broken, the meter will read infinite ohms due to an open circuit. Most digital meters these days will read "OL" for "overload" in this situation.
If the conductor in the glass is broken, You might not be able to fix it. Many newer cars have the wire on the surface of the glass, and it is possible to make repairs when necessary. The Rover backlights I've seen have the heating elements sandwiched between layers of glass where you can't get to them. Also, all of the ones I've seen so far (not many) have had obvious broken elements between the layers of glass.

Conductive paint
This method fixed the heat on the rear window on a Rover 200:
Leave everything off, flip up the tailgate and use the resistance scale on the multimeter. By placing the probes against the tracks it is possible to determine which tracks were broken because of a large variation in the measured resistance. Note that we're talking from 0.1 to about 0.5 ohm. What happens is that the ohmmeter either measures the resistance along the single track (if the track is whole), or of the rest of the "network" (if the track is broken).
Some notes:

* it's easy to scratch the track, thereby increasing its resistance.

* this method only works for tracks that are exposed on the (inner) surface.

* conductive paint works, but make sure you clean the surface properly and follow the instructions. Given the price of the product, you might expect enough silver-loaded paint to cover the entire window, but in practice there is only sufficient to maybe repair a dozen minor cracks.