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How to choose a radar detector

What to look for in a radar detector

I've been with Crutchfield since 1999, where I began as one our advisors, helping our customers choose new gear. After a couple of years, I moved to the writing team where I spent a decade researching new products and getting hands on with car stereos, amplifiers, speakers, and subs. Yeah, I've been doing this for a while.

For the past few years, I've been the managing editor of Crutchfield's Car A/V web article content. I couldn't ask for a better job — we get to play with car audio gear every day! I'm a Virginia native from the heart of the Blue Ridge Mountains. Outside of work, I love listening to music, playing board games, and installing new audio systems for my friends.

More from Robert Ferency-Viars

Escort Passport Max 2

Newer detectors, like the Escort Passport Max 2, are packed with features like GPS technology and Bluetooth compatibility.

The freedom to relax and drive with confidence — that's what an investment in a radar detector can give you. Today's models combine simple, ergonomic design with up-to-the-minute technology, including GPS, Bluetooth® compatibility, and smartphone integration. They can offer you affordable, convenient protection, not only from speeding tickets but often from driving hazards as well.

Some features to look for:

  • Type of detector: There are three types of radar detector: corded, cordless, and remote-mount. Corded detectors usually mount on the windshield via suction cups, and provide the best range of detection. Cordless detectors are transported easily between vehicles, and provide a cleaner installation than corded models. Remote-mount detectors are permanently mounted to your vehicle, providing a clean installation that's virtually undetectable by thieves.
  • City Modes: City mode reduces the range or sensitivity so that you get fewer false alerts from sources of signals similar to radar guns, such as automatic door openers; this feature is helpful for urban driving.
  • Laser detection: A detector with one laser sensor can detect laser beams in front of you, but not behind you or off to the sides. 360-degree laser detection uses two sensors to look for laser pulses to the sides and behind you. Models with 360-degree laser detection tend to be more reliable, but more costly.
  • VG-2 and Spectre protection: These are shielding technologies that let you know when police are using radar detector detectors (RDD). Spectre is a more advanced RDD technology, which has evolved to the point that it can be very difficult to protect yourself from . Some detectors offer stealth protection, which warns you and then shuts down the detector, while more expensive detectors offer Invisible protection — they may be shielded from VG-2, Spectre, or both, so they can continue operating without being discovered.
  • Digital voice alerts: A voice alert tells you what your radar detector has picked up. You don't have to take your eyes off of the road to look at the detector's display.
  • "Instant-On" Protection: Practically speaking, you can't really defend yourself against Instant-On radar; if it's been aimed at you, your speed has been measured by the time your detector gives an alert. However, if the radar was targeted on a car ahead of you, a detector with sensitive K-band reception will alert you. High K-band sensitivity is what allows manufacturers to promote a detector as giving Instant-On Protection.

VG-2 and Spectre RDD

In some localities, it's illegal to use a radar detector, and many areas have regulations against using detectors in commercial vehicles. Therefore, police have developed "radar detector detectors," referred to as RDD. These devices pick up oscillations emitted by the receivers in radar detectors, and inform police that a radar detector is being used. Many manufacturers now have models that are specially shielded to eliminate most of these emissions, or will shut down when they detect a RDD system in use.

VG-2 is a common type of RDD technology, and it works by detecting the oscillations on a single frequency band. Most detectors today are built to protect themselves from VG-2 detection, but a more sophisticated type of RDD technology, known as Spectre, has proven more difficult to circumvent. This is because Spectre operates on several frequency bands and can pick up more emissions from a radar detector. There are detectors on the market now which do offer Spectre invisibility, but Spectre's an evolving technology so not all detectors will be able to defeat all levels of Spectre.

Radar with GPS

Recent developments in GPS technology have empowered radar detectors with more functionality than ever before. GPS stands for global positioning system, a satellite network that communicates with devices to assist in ground-based navigation applications. GPS devices in cars communicate with satellites while moving. These devices measure speed, location, and direction down to a few feet. They can often also store location information to mark important points on the map.

GPS radar detectors can calculate where they are and how fast they're going at any time while they are communicating with the GPS network. This is a powerful advantage over normal radar detectors because even though they can tell you when radar is in use around you, they have no way of knowing how fast your vehicle is traveling.

Some GPS detectors can adjust their sensitivity depending on how fast the vehicle is going, which reduces the need to manually switch between city and highway modes. They can also alert you when you are traveling over a set speed limit for your own safety.

Some GPS radar detectors can be programmed to "remember" areas that you drive past and alert you when they are approaching. If you drive past an area with a suddenly steep drop in the speed limit, the detector can warn you ahead of time so you can adjust your driving accordingly. Or you can program it to remind you of areas where there are red-light or speed cameras or frequent speed traps. Some detectors even offer access to a downloadable database of known camera and enforcement locations, which you can then program the detector to alert you to.

Smartphone compatibility

As with most other technologies, there are now ways to integrate your radar detector with your smartphone. Apps are available for iOS and Android™ platforms that let detectors work in conjunction with your smartphone, typically to give you alerts provided by other app users for enforcement locations in your vicinity. Some apps also let drivers highlight enforcement areas they encounter, so that other users can be alerted as well. There are also radar detectors that transmit alerts directly to your smartphone via Bluetooth® connection, allowing the detectors to have an even smaller footprint because they don't have a display themselves.

How radar detectors work

Think of a radar signal as a beam of light from a flashlight. When you shine a flashlight at an object, your eyes perceive the light reflected from the object. Now imagine yourself as the object being illuminated. You can see the light from the flashlight from a much farther distance than the person with the flashlight could ever hope to see you. That's because the beam loses energy over distance. So while the beam has enough energy to reach you, the reflected light doesn't have enough energy to travel all the way back to where it started.

Police radar guns "see" a vehicle by transmitting a microwave pulse. Then they make use of the Doppler Effect: the frequency of the transmitted pulse is compared to the frequency of the reflection, and speed is calculated by using the difference between them.


Speed is calculated when a pulse is reflected to the radar transmitter.

That's the idea behind radar detectors. They look for radar "beams" and find them before they can return a strong enough reflection to "illuminate" you. Detectors use something called superheterodyne reception to accomplish this. Radar detectors are essentially microwave radio receivers that make noise or flash lights when they sense an incoming signal on specific frequencies. Superheterodyne reception allows detection of radar around curves or over hills, and it extends detection range straight ahead.

Different types of radar

The Federal Communications Commission has dictated that police radar must operate on specific frequency bands:

radar bands

X-band: 10.5 - 10.55 GHz

Dating from the 1950s, X-band radar is the easiest to detect because of its lower frequency and higher power output. Depending on terrain, temperature and humidity, X-band radar can be detected from a distance of 2 to 4 miles, yet it can only take accurate readings of speed from a distance of 1/2 mile or less.Unfortunately, police radar is not the only source of X-band signals. Garage door openers, microwave intrusion alarms, microwave towers, and other high-tech equipment can fool a radar detector into giving off an X-band alert. Filters and redundant sampling are used to combat this "falsing."

K-band: 24.05 - 24.25 GHz

K-band, the most common type of police radar, made its appearance in 1978. The first K-band hand-held radar guns could only be used from a stationary position. Later, a "pulsed" version was introduced that could be used from a stationary or moving vehicle.K-band radar waves have a relatively small wavelength and so are more easily absorbed by water molecules in the air. At the power level found in police radar guns, K-band has an effective clocking range of about 1/4 mile. Depending upon terrain (around a corner, over a hill, etc.), K-band waves can be detected from a range of 1/4 to 2 miles.

K-band guns also have what's known as "Instant-On" radar. This is basically a kill-switch option which keeps the transmitter in "hot standby" mode, ready to be activated by an officer when the target is within 200-300 yards. If it's been aimed at you, your speed has been measured by the time the detector alerts you. If it is being used to target vehicles ahead of you, your detector may provide a warning in time for you to adjust your speed.

Ka photo cop and Ka wide-band: 34.2 - 35.2 GHz

In 1987 the FCC allocated a frequency on yet another band, Ka, for police radar use. With that came the introduction of photo radar (also known as "photo-cop"). The photo-cop system works at 34.3 GHz and combines a Ka-band radar gun with an automated camera. A vehicle approaching at or above a predetermined speed will trigger the camera. The photo shows the front of the vehicle, license plate, driver's face, the date, location, and time. The unit can clock and photograph up to 200 vehicles per hour. Alleged speeders are not stopped. The film is processed and a citation is mailed to the registered owner of the vehicle, ordering him or her to pay the fine or appear in court.

Photo-cop's effective range is 120-300 feet and it transmits a continuous signal which is a plus for radar detectors. The distance at which it can be detected varies depending upon a detector's Ka-band sensitivity. Better detectors can typically sniff out a photo-cop system 1/4 to 1/2 mile away. Industry sources predicted widespread interest and expanded use, but that has not been the case —; only a handful of cities use photo radar. Legal controversies along with prohibitive expense have caused officials to stick with more traditional methods of speed detection. The FCC later expanded Ka-band radar use to a range of 34.2 - 35.2 GHz. This became known as Ka Wide-Band.

Ka super wide-band: 33.4 to 36.0 GHz

The introduction of the "stalker" radar gun raised the stakes in the detection game. Unlike all previous guns, the stalker can be FCC licensed for any frequency in the Ka-band between 33.4 GHz to 36.0 GHz, and so cannot be picked up by detectors designed only for X, K, and photo radar. Stalker guns are being used across the country. In response, manufacturers developed detectors with "Super wide-band" technology that sweeps all of the Ka-band allocated to radar, as well as providing continued protection against X, K, and photo radar.

Ku-band radar, which is not indicated in the diagram on the previous page, is used primarily in Europe and not often seen in the United States. Its frequency here is 13.45 GHz, as established by the FCC. Some companies do tout the ability of their detectors to track the Ku-band radar, despite its limited applications in America.

Laser detectors

Laser speed guns determine speed differently than radar guns. A series of light pulses is transmitted, and the difference in time between pulses and reflections is used to calculate speed. This all takes place very rapidly (at the speed of light, as a matter of fact). A single pulse typically requires only a few nanoseconds to transmit and return. The advantages of a laser gun are compelling: the laser light beam is far narrower than a radar beam, allowing more accurate pinpointing of a specific vehicle; and the total time needed for capturing a speed reading is less than half a second versus 2 to 3 seconds for radar.

The drawbacks are also important to note: laser guns are very expensive, they can't be used from a moving vehicle or from behind glass, and accurate aiming requires a tripod or a very steady hand.Despite initial claims to the contrary, a laser gun is detectable. And as the laser beam moves away from the laser gun, it widens and becomes even easier to detect. Vehicle speeds are typically measured at roughly 1,000 feet (1/5 mile); at that distance the laser beam is over 3 feet wide. Many of the laser detectors in use have a working distance of approximately 1-1/2 miles (at that distance a laser gun's beam covers two lanes of traffic).

Factors affecting range

According to a Car & Driver study, a significant loss in detection range occurs when vehicles contain windshields with metallic film embedded, and when commercially available tint films are applied.

Radar detection range is most affected by windshields with metallic film solar-barrier treatments .These treatments are found in Ford products with Instaclear windshields, GM products with PPG and Everclear windshields, and in some high-end imports. In these vehicles, detection capability drops by a startling 95 percent.

Laser detection range is always affected by glass, sometimes losing up to 80% of its sensitivity. It's also affected by tint films — the darker the tint, the more loss. Some tint films contain a metallic layer, and these can reduce radar detection capability by as much as 37 percent.

  • Ed Johanson from Riverton

    Posted on 2/21/2016

    Years ago I read that the VW Beetle and Stingray had near stealth reflectivity. This gave a driver a chance to make speed adjustments.

  • Beni from Dallas

    Posted on 4/3/2016

    VERY helpful, especially for someone who has never known the details behind the functionality of radar and radar detection. Thanks very much for making my shopping more informed!

  • Alpha from New York City

    Posted on 5/11/2016

    Good stuff, I learned pretty much everything I wanted to know about radar detectors.

  • Bug from New York

    Posted on 9/24/2016

    Very Informative! Thank you

  • brrr..!

    Posted on 10/26/2016

    Fantastic article. Thank you so much!

  • Stephen from Stl

    Posted on 1/1/2017

    I never knew how they worked till now Thanks

  • simon marcellino from Covent Garden

    Posted on 2/27/2017

    Some things to consider when looking at detector reviews are how the range was calibrated. While many detectors can, in theory, detect a radar signal up to five miles away, in the real world those conditions are rarely ever met. So, when you are considering a detector, look into how the detector was tested.

  • Oscar from Los Angeles

    Posted on 3/5/2017

    Great article very informative

  • Rose from Memphis

    Posted on 4/3/2017

    Which radar can we use legally.

  • Alexander Hrabe from Crutchfield

    Posted on 4/10/2017

    Rose, legality varies state to state. Depending on where you plan on using a radar detector, give us a call for more information on the right one for you.

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