HOW TO BUY RADAR DETECTORS

Radar detectors are intended to pick up radar from speed guns and are legal in most states (check your local laws before ordering).
See "Law" for more information regarding state laws.

The idea behind radar detectors is that they look for radar "beams" and find them before they can return a strong enough reflection to "illuminate" you. Superheterodyne reception is used to accomplish this and allows for the detection of radar around curves or over hills, and it extends detection range straight ahead.
Radar detectors give you the freedom to relax and drive with confidence. They can offer you affordable, convenient protection from speeding tickets and from driving hazards, as well.

Radar Bands and Radar types

There are different types of radar. The Federal Communications Commission has dictated that police radar must operate on X-Band Radar: 10.5 - 10.55 GHz.
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, 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 too but there are ways to combat this “falsing”.

K-Band is the most frequently used radar frequency band: 24.05 - 24.25 GHz. K-band radar waves have a relatively small wavelength. At the power level found in police radar guns, K-band has an effective clocking range of about 1/4 mile. Depending upon terrain, K-band waves can be detected from a range of 1/4 mile to 2 miles. K-band guns also have "Instant-On" radar, which is basically a kill-switch option that 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-Band is another band allocated for police radar use. Ka-Band incorporates Ka-band, Ka Wide-Band, and Ka Super Wide-Band. With Ka 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.

POP Mode is a normal K or Ka band radar signal which travels back and forth from the radar gun to a target in less than 1/10th of a second. Most radar detectors older than 2 years and cordless radar detector models can not see this signal because it is just too fast. Many of the newer models do offer protection for this.

The Ka Wide-Band was born when the FCC expanded Ka-band radar use to a range of 34.2 to 35.2 GHz. Unlike all previous guns, the “Stalker” detectors 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 in more than half the country.

Ku-Band radar ranges between 12 and 18 GHz. It is used primarily for satellite communications in aerospace and broadcasting. It is used mostly in Europe and is not seen much in America. Ku is set at 13.45 GHz by the FCC and has only recently been introduced to the U.S. for speed detection.

Laser Detection

Laser detection is a detector with one laser sensor that can detect laser beams in front of you, but not behind you or off to the side. 360-degree laser detection uses two sensors and can detect laser pulses to the side as well as behind.

VG-2 and Spectre RDD

In some states it is illegal to use a radar detector or laser detector, and many areas have regulations against using detectors in commercial vehicles. Because of this, police have developed "radar detector detectors" (RDD). These devices inform police that a radar detector is being used. Many manufacturers now have models that are specially shielded 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 radar detectors today are built to protect themselves from VG-2 detection, but a newer 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 radar detectors on the market now which do offer Spectre invisibility.

Radar Scramblers and Laser Jammers

Scrambler/Jammers disable radar/lidar detectors. There are two types: active and passive. Active jammers transmit a new signal of their own which confuse police speed devices AND they can work at any distance. Passive jammers take the original X, K, Ka, Ku, Xu frequencies and add an FM chirp which confuses the signal inside the gun, giving you time to adjust your speed.

Factors Affecting Range

A 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 in which 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.

Mountings

Most modern radar detectors offer 360 degree full band protection, POP Mode detection, VG-2 cloaking, and City/Highway modes. Corded detectors, cordless detectors, remote-mount detectors and motorcycle radar detectors are different types of radar detectors that are available.
Corded detectors mount on windshield with suction cups, cordless radar detectors can be transported between vehicles, remote-mount detectors are permanently mounted to the vehicle making them virtually undetectable to thieves, and motorcycle radar detectors are specifically designed to allow for easy mounting on motorcycles.

Features

Some advanced radar detectors have additional features such as Laser/Radar Scrambler,   Stay Alert,   Text Display,   Voice Alert,   Compass,   Strobe Alert,  and Spectre Alert.

City/Highway Mode
City Mode turns down the sensitivity so that there are fewer false alerts from non X-band emissions encountered in urban areas (some radar detectors will still beep when a signal is detected, however it will automatically enter Quiet mode after one or two beeps if the signal is weak). Highway Mode does not filter out any band, or automatically silence weak signals.

Audio/Visual Alerts
A series of “beeps” that grow faster as you near the radar source.

Text Display
The Text Display spells out what form of speed detection you are up against.

Dim/Dark Display
Dims or eliminates illumination on alarms and controls to keep the detector inconspicuous while driving at night.

Digital Voice Alerts
Voice Alerts tell you what your radar detector has picked up, keeping the driver from having to look away from the road to look at the detector.

Mute
Turning the audible alerts down or off while keeping the visual alerts.

Selectivity
A detector's ability to detect police radar while ignoring the presence of automatic garage door openers, microwaves, and other items which may operate on closely neighboring frequencies. A good radar detector offers high selectivity as well as being highly sensitive.

GPS Radar Detectors
GPS Radar Detectors can calculate where they are and how fast they are going at any time while they are communicating wit the GPS network.

Instant On Protection
K-band radar guns have what's known as "Instant-On" radar. This keeps the transmitter in "hot standby" mode, ready to be activated by an officer when the target is within 200-300 yards. You can't really defend yourself against Instant-On radar. High K-band sensitivity is what allows manufacturers to promote a detector as giving Instant-On Protection.

Safety Warning System
Radar detectors with Safety Alert transmits a signal to alert you of changing or potentially hazardous road conditions.

Law

United States law varies from state to state, but detectors are generally legal in private vehicles under the Communications Act of1934 and illegal in commercial vehicles by DOT regulation (49 CFR 392.71.)
Exceptions:
Illegal in all vehicles: Virginia, Washington D.C., U.S. military bases.
Illegal in commercial vehicles under state law: Illinois, New York (specifically, commercial vehicles over 10,000 lb. and all vehicles over 18,000 lb.)
Indirectly illegal: Minnesota and California (illegal to hang anything from the windshield with suction cups; however both dashboard and visor mounting is allowed.)