Could it have been laser? I know that when laser is used to read a speed on a vehicle, it's usually aimed at the license plate, as plates are quite reflective. I don't know if you've heard of a product called the Defuser Plus. But it's a frame that mounts on over your license plate that supposedly jams laser. I've heard it's about 40% affective from tests that have been done on it. I'm thinking about getting one.
Anyway, If you had your front plate off, this might explain why you didn't get a reading untill you were "on top of it."
Then again, I'm not sure if laser would be used in an automated system like this, as you would think there would need to be a police officer manually aiming it at your plate.
PS. Sorry for deviating from the deviated topic
