Radar detectors are electronic devices used to alert drivers of police presence and speed detection hardware. They’re great tools for drivers with a heavy foot to avoid speeding tickets, but are they legal?
How Radar Detectors Work
Radar is an acronym for Radio Detection and Ranging. Several vital components enable radar systems to detect distant objects: A frequency source that creates a low power signal at the operating frequency of the radar A radar transmitter that amplifies the power level of the signal from the sources A radar antenna used to broadcast or transmit the signal from the radar into the air A radar receiver that can detect a return signal that has bounced off of an object A radar signal/data processor, which translates the returned signal to identify objects, their distances, and their speeds Power supplies that provide power to each of the radar components
Radars operate in two modes: transmit and receive. Transmit mode means the radar is sending a signal into the air, and receive mode means the radar is not transmitting any more and is instead listening for a return signal.
Radar signals are emitted in a series of short bursts called pulses. Pulses travel outward away from the antenna until they encounter objects in their path. The return pulses travel back to the radar and are processed by the receiver and signal processor. The radar can detect the object’s relative position, direction, and speed by sending related signals and listening for their return. It does so by listening for the return signals and establishing how long the return signal takes to bounce off the object.
When a police officer has a radar gun to detect the speed of cars on the road, it uses a phenomenon called the Doppler effect. When it occurs, the radio wave frequency changes depending on the car’s motion relative to the radar. If a vehicle is moving toward the radar, the frequency increases. The shift in frequency indicates how fast the vehicle is moving.
Radar detectors pick up the specific frequencies used by radar guns. Radar detectors can often pick up the radar gun’s radio wave transmission before the car comes close enough to the radar gun to have its speed detected. This is thanks to radar signal emissions speed out in the air as they move away from their source.
When a radar picks up the radar signal, it sounds an alarm and lights up to notify the driver that a radar gun is ahead. More advanced radar detectors can not only detect police radars but can also throw off the police radar by transmitting a scrambled signal called a jamming signal.
Radar detectors are not 100% accurate as they can pick up false alerts.
Additionally, police officers use laser speed guns, known as LIDAR, to detect vehicle speeds. Standard radar detectors cannot detect LIDAR guns, but LIDAR detectors can. However, their effectiveness is not as high. Like radar detectors can have radar jammers, LIDAR detectors can be equipped with laser jammers.
Are Radar Detectors Legal?
Yes, radar detectors are generally legal in the United States. This is because detectors are intended for drivers to be mindful of their driving speeds. However, radar detector laws vary from state to state.
Opponents of radar detectors say that they can encourage overspending among drivers and allow dangerous and reckless driving. They also argue that drivers will follow set speed limits and drive more carefully without radar detectors.
Virginia is currently the only U.S. state where radar detectors are illegal to use. The District of Columbia does not allow radar detectors either. Additionally, radar detectors are prohibited in all commercial vehicles and all vehicles 18,000 pounds or heavier.
Some states don’t allow radar detectors because they can distract the driver, especially if there is a false alert, and that radar detectors can obstruct the driver’s view. Because of this, the following states have banned mounting radars on windshields:
While most states allow radar detectors, the use of radar jammers is not allowed in any state due to federal law. However, laser jammers are allowed in some states. Laser jammers are permitted in the following states: