Depends on what you are driving. If you are driving a normal car or truck it is only illegal in Virginia and Washington D. C. Though, it can also be illegal in Minnesota, California, and New York for obstructing your vision.
Radar detectors in non-commercial vehicles are illegal in Virginia and Washington, DC. Radar detectors in commercial vehicles are illegal in all U. S. states, Washington DC and through most of Canada, and have been since 1995.
At last look, this was illegal in all vehicles in Virginia and DC, for commercial vehicles in Jersey, Illinois, NY, indirectly in Minnesota, California and NY (items affixed to windshield)
