not sure on the law. mark might know
As far as triping the light:
most stoplights are magneticly activated (the mass of metal frame in a car creates a magnetic field that the sensor uner the pavement picks up. motorcycles lack in this large quanity of metal, and as such dont trip lights. i would assume that this device emils a magnetic field that will trip the light.
on a side note, any mass of metal on earth emits a signature or patern as it passes through the earths magnetic field. The russians knew this, and aplied a countermasure to its destroyers in its naval fleet by placing magnetic coils in them to "erase" this signature, making them harder to find.