The Commonwealth of Virginia and the District of Columbia are the two states in which it is illegal to use a radar detector. If you are caught using one, the police officer can give you a ticket and take the radar detector from you. Police in Virginia and Washington, D.C., have devices they can use to determine if you are using a radar detector.

The United States Department of Defense and the U.S. Department of Transportation have regulations that prohibit drivers from using radar detectors, regardless of the state in which they travel. The DOD traffic safety program prohibits anyone from using a radar detector on any military base in any location. It also prohibits the sale of radar detectors on U.S. military bases. DOT regulations prohibit the operators of all commercial vehicles from using radar detectors.

Using a radar jammer violates federal law under the Communications Act of 1934 because it is illegal to broadcast radio waves over FCC frequencies without a license. The radio signals a radar jammer sends out can also disrupt police radios. If you're caught using a radar jammer, you could be charged with a felony. Laser jammers emit light, not radio waves, and therefore aren't illegal under federal law, but they are illegal in 12 states: California, Colorado, Illinois, Minnesota, Nebraska, Oklahoma, South Carolina, Tennessee, Texas, Utah, Virginia and Washington, D.C.

Radar detectors usually come with a holder, plastic suction cups and a visor clip. You can attach the holder to the windshield using the suction cups and insert the radar detector into the holder so its reception is unobstructed. If you're driving in either California or Minnesota, use the visor clip instead. It's illegal in both states to attach anything to the windshield that could limit your view of the road, such as cell phone cradles and radar detectors.