From new windshield wipers to extra power outlets, there are plenty of accessories available to make life easier for motorists. And if you’re planning a road trip, one common recommendation is a police radar detector. Anyone with a history of speeding tickets would likely consider it a must-have. But is it an accessory worth buying?

How does a radar detector work?

Nowadays, cops aren’t the only road-users with access to radar. If your car has adaptive cruise control, blind-spot monitoring, and/or lane-keeping assist, it uses radar, Car and Driver reports. And it’s even spreading to motorcycles.

Radar works by bouncing high-frequency electromagnetic waves at an object. When the waves return, a detector measures how much their speed and frequency have changed. This information lets the radar ‘gun’ calculate how fast the object—in this case, a car or motorcycle—is moving.

Commercial radar detectors are basically stripped-down, passive versions of police radar guns, LifeHacker explains. They pick up on the radar signals emitted by cops and traffic-light cameras. And the best ones cover wider frequency ranges and indicate signal origin points, The Drive reports. At least, in theory.

The rise of ADAS features, besides raising vehicle repair costs, has also rained havoc on radar detector accuracy, Road & Track reports. Not only do more cars come with radar-emitting devices, but many of those devices operate on police frequency bands, Autoblog reports.

Cheap radar detectors often can’t filter through the ‘noise,’ The Drive explains, which results in annoying false positives. Some of the more expensive models, though, have software-based and/or hardware-based ways of separating an ADAS feature from a cop, Autoblog and R&T report.

Are police radar detectors legal?

It’s worth pointing out that police don’t only rely on just radar anymore; some speed traps use lasers. However, just as radar detectors have gotten better at eliminating ADAS noise, so too have they started detecting lasers, The Drive reports. Some even feature built-in laser jammers, Motorcyclist reports. But while that last feature seems useful, it may come with some unexpected legal consequences.

To be clear, in almost every US state, it’s legal to use a radar detector in a non-commercial vehicle, R&T reports. Provided you aren’t driving through a military base or national park, the only places where detectors are illegal are Virginia and Washington, D.C. Though admittedly, California and Minnesota have rules against mounting things on windshields, including radar detectors, Autoblog reports.

However, it’s slightly more complicated where jammers are concerned. Radar jammers, while they exist, are fully illegal per federal law. Laser jammers, though illegal in many countries outside of the US, are regulated by state laws. As a result, they’re only illegal in California, Colorado, Illinois, Minnesota, South Carolina, Tennessee, Texas, Utah, and Virginia, YourMechanic reports.

Should you get one for your car or motorcycle?

Although many radar detectors are designed for use in cars, motorcycle-specific ones are available, Cycle World reports. But does that mean it’s worth getting one for your car or bike?

The best radar detectors can be pricey. While budget ones can cost around $200-$300, you’ll have to spend at least $500 to get features filtering, built-in Bluetooth, and app connectivity, R&T reports. And if you something like WiFi and Waze, prepare to spend closer to $750, Car and Driver reports.

To be clear, MotorBiscuit does not recommend or endorse speeding. But if you want a detector as a ‘peace of mind’ tool, that’s different. You’ll have to weigh the mental relief against the possibility of false positives. At which point, you’re in the $500-$750 range. Whether or not that’s worth it is up to you.

Personally, I’ll just stick to following the speed limit.

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