Here are all the facts regarding who can use a radar detector and where: Under federal law, the use of radar or laser speed detectors is illegal in all commercial vehicles over 10,000 pounds. Radar detectors are illegal to use in any vehicle in the District of Columbia. Radar detectors are illegal to use in any vehicle in the state of Virginia. Radar detectors are illegal to use in any vehicle while on any military installation. That’s it. In all other states radar detectors are completely legal to use in a passenger vehicle.