I was at SEMA a few years ago and the Blinder brand had a booth there. Although currently ranked behind the Laser Interceptor brand it was still impressive.
Very small and easy to hide, they work by acting like a laser version of a strobe light sending multiple beams back causing erratic readings. Best used with multiple transceivers for front,rear, and side coverage.
The only reason it is illegal is because you have an advantage in the cat and mouse game.