Virtually all patrol cars are equipped with a traffic radar device of one kind or another, some are micro wave others are lasers. Depending on the model of the device, it can detect and record the speed on an on coming vehicle while the patrol car is moving or while the patrol car is parked. Some devices can have an extra detector in the rear window of the patrol car to detect the speed of vehicles approaching from the rear. Most of the traffic radar devices can be removed from the patrol, and be used as a hand held device, with no patrol car near by. The range of the device is determined by the model used. Some are designed for city driving and have a short range of two or three hundred yards. Those used by Highway patrol units can range out to close to a mile. The laser devices can be almost unlimited. Most units will be on constantly and can be set to alert the officer when a certain speed is met or exceeded, then the officer simply locks in the offender’s speed. Some devices, like the laser, can be aimed at one vehicle in a group of vehicles and capture just that car’s speed. Some devices can be totally automated. Europe uses such machines. The radar catches your speed, a camera takes your picture, and you are mailed a speeding ticket. All done by computers. . ., don’t even need the cop to write the ticket.

If you are asking about a device that would tell the officer if you had a radar detector in your vehicle. No, most patrol cars do not have such a device. No need to since most of them do not work all that well.