We Tested Cobra’s New $120 Radar Detector. Is It Any Good?

If you struggle to justify buying a radar detector for $300 or $500 or even $800 when the free Waze phone app is so good at sniffing out Smokey, you might be interested in the Cobra RAD 390. At just $120, the new radar detector costs less than a week’s worth of groceries while providing additional peace of mind by covering Waze’s blind spots.

Cheap radar detectors need to be approached with skepticism. The worst of the bunch behave like random noise generators, bleeping and blooping constantly, except when they don’t and you end up with a speeding ticket. Whether or not the RAD 390 is worth your money then comes down to one question: Does it work? I’ve been living with and using Cobra’s newest radar detector for more than a month, and while it’s not for everyone, I can also confirm that it’s not a random noise generator, either.

What You Get (and Don’t) for $120

The RAD 390’s budget price shows up in both its feature list and in its build quality. One MotorTrend editor who knew nothing about the Cobra and its price took one glance at it and called it a “truck-stop radar detector.” The simple controls and display give away just how basic it is. There’s a thumb wheel for dialing in the volume plus three buttons that allow you to adjust the sensitivity, dim the display, and mute an alert.

Cobra RAD 390 Radar Detector (presently $119.95): BUY NOW ON AMAZON

You can also get a sense of the RAD 390 based on what it doesn’t have. There are no arrows to indicate where the radar signal is coming from because the RAD 390 has only a single, forward-facing radar antenna. (It can pick up laser coming from the front or rear, but a laser alert from any radar detector has limited value. By the time the detector is squawking, the cop almost certainly has your speed.) The RAD 390 can’t be paired with a phone app and it doesn’t have a GPS antenna to lock out radar signals from automatic doors and other sources of false alarms.

Cobra did come up with one novel idea that the rest of the radar-detector industry needs to copy. The RAD 390 draws power through a six-foot USB-C cable that can be plugged into a car’s USB-C ports or an included 12-volt outlet adapter. Most detectors still use phone-jack power ports and coiled cables, the same as they did when college kids were dancing to the Macarena on spring break. It’s about time somebody recognized that 12-volt outlets are disappearing in modern cars and those that survive are rarely located in a convenient spot for running a radar detector.

On the flip side, the included mount is the result of cost-cutting gone too far. It sticks to the windshield using double-sided tape that gives you one shot at getting the semi-permanent installation right. Cobra includes a rectangle of window-cling film for a temporary install, but there’s no getting around the fact that whatever you stick the mount to the first time is the only thing it will ever stick to. Most buyers will want to spend another $15 for a generic sticky-cup mount from Amazon.

But Can It Sniff Out a Cop?

None of this matters, of course, if the RAD 390 can’t pick out a cop lying in wait amidst all the automatic doors and radar-emitting cars in the modern world. We put the RAD 390’s range and responsiveness to the test using a Ka-band Stalker II radar gun in three different scenarios. In two tests on a long, straight road with the radar gun pointed toward and away from the approaching target car, the RAD 390 gave roughly half the alert distance of top-tier radar detectors like the Uniden R8w, Escort Redline 360C, and the Valentine One Gen2. All of these, however, cost several hundred more, and the Cobra did offer enough warning that an attentive driver would be able to hit the brakes before the Stalker could pick up a speed reading.

The RAD 390 struggled in our third test, in which our “police officer” was waiting around a 90-degree bend on a rural road. This test is challenging for all detectors because the signal is traveling perpendicular to the stretch of road our bogey is driving on, so there’s little chance of picking up the edges of the signal until you’re right on top of the source. The RAD 390 alerted literally at the last second as the target car rounded the corner. The high-end detectors also gave relatively short warnings here, too, but provided a couple more seconds of advance warning.

Cobra RAD 390 Radar Detector (presently $119.95): BUY NOW ON AMAZON

The other trade-off, as you might expect, is that the RAD 390 is noisier than the $500 and $800 detectors that offer more advanced filtering. Cobra’s $120 detector can be toggled between three standard sensitivities plus an Extreme mode with the fastest response times. The two most sensitive settings don’t do any filtering. If the unit detects a radar signal, it will beep. The quieter of the two modes aims to reduce the number of false alerts, but even the least sensitive setting was occasionally duped by the blind-spot monitors on surrounding traffic. More expensive detectors offer advanced filtering that makes them quieter, which is a big benefit for anyone who will use the device for every drive.

Based on that experience, the Cobra RAD 390 is best suited to drivers who use a radar detector only periodically—say on long road trips or when driving in unfamiliar places—to augment Waze rather than someone who will use it every single day. Crowdsourced cop-spotting apps can’t protect you from police who are on the move and they aren’t dependable on rural roads with light traffic. Then there’s the possibility that you’re the first person to mark a cop on Waze—moments after being pulled over. A Cobra RAD 390 is a cheap insurance policy that, in these situations, significantly increases the odds you pick up police radar before it can read your speed.

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