How about a "Sauron's Eye" for your car? 

Playback speed was increased to 300% for the action scenes both to give a Charlie Chaplin, silent slapstick movie feel and to speed up the rather dull sparks in that light. I did try to randomly interpolate 100 frames (manually!) to give the effect of a uniform field but it wasn't convincing.

Actual rotation speed is about 10 seconds per revolution which is easy for thieves to avoid I guess.

I did night time shots with great looking sparks but there was severe motion blur with the reduced frame rate and you couldn't see the bad guy. The brightest sparks are to the dummy thief (stuffed with old blankets) who had a grounded wire in his torso.

Smoke was from a smoke generator controlled by Chris in the car and timed to smoke at the time of the sparks. It is the blue thing under the front bumper.

I wet the ground to intensify the sparks but didn't turn off the tap properly so there is a bit of a river through the scene.

 

My wooden counterweight is on fire here at the top of the coil.  It's quite safe to be in the car although my son was apprehensive.  This was a Hyundai Getz hire car (as I don't own one) and it still works. I did get extra insurance "in case". Of course a Tesla Roadster from Tesla Motors would be the ideal car for this or a De Lorean.

Construction photos. There is a rod projecting out the top of the TC and the sparks will come from the tip of the rod. If that rod is bent so that it nearly touches the ground it will spark to ground.  If you rotate the rod around the car it will form sparks as it traces out a circle.  If you take a long exposure then the sparks will all be on one photo giving a ring of sparks.

Tesladownunders Car Theft Protection (red car version)

Tesla Car Theft Protection (video)

 Some behind the scenes shots during production.