The Electronic Code of Federal Regulations states that radar detectors in Washington D.C. (and Virginia) are prohibited. Radar detectors are prohibited in all areas, including commercial vehicles and military bases. California and Minnesota do not allow windshield mounts. You should check your state regulations before you buy. Although they may be illegal in certain areas, installing a radar detector in your car doesn't constitute a violation of the law. Insurance companies won't punish drivers who have one.