Radar detector

Description

One device law enforcement use to measure the expected speed of a moving vehicle is called Doppler radar, and it uses the Doppler effect to measure the relative speed of a vehicle. Namely, Doppler radar works by beaming a radio wave at the vehicle to then measure the expected change in frequency of the reflected wave (that bounces off the vehicle). Many times, law enforcement employ Doppler radar in their hand-held radar guns, on their vehicles, as well as on fixed objects such as traffic signals.

Radar detectors use a superheterodyne receiver to detect these electromagnetic emissions from the radar gun, and raise an alarm to notify the motorist when a transmission is detected. False alarms can occur however due to the large number of devices, such as automatic door openers (such as the ones at supermarkets) and adaptive automotive cruise control, that operate in the same part of the electromagnetic spectrum as radar guns.

In recent years some radar detectors have added GPS technology. This allows users to manually store the locations where police frequently monitor traffic, with the detector sounding an alarm when approaching that location in the future (this is accomplished by pushing a button and doesn't require coordinates to be entered). These detectors also allow users to manually store the coordinates of sites of frequent false alarms, which the GPS enabled detector will then ignore. Some GPS enabled detectors can download the GPS coordinates of speed monitoring cameras and red-light cameras from the Internet, which are contained in the TRINITY database. An interstate traveler could receive an alert when approaching a location with a speed monitoring camera.

Counter technology

Radar guns and detectors have evolved alternately over time to counter each other's technology in a form of civilian electronic "warfare". For example, as new frequencies have been introduced, radar detectors have initially been "blind" to them until their technology, too, has been updated. Similarly, the length of time and strength of the transmissions have been lowered to reduce the chance of detection, which in turn has resulted in more sensitive receivers and more sophisticated software counter technology. Lastly, radar detectors may combine other technologies, such as GPS-based technology with a point of interest database of known speed trapping locations, into a single device to improve their chances of success.

Radar detector detectors

The superheterodyne receiver in radar detectors has a local oscillator that radiates slightly, so it is possible to build a radar-detector detector, which detects such emissions (usually the frequency of the radar type being detected, plus about 10 MHz). The VG-2 Interceptor was the first device developed for this purpose, but has since been eclipsed by the Spectre III and Spectre Elite. This form of "electronic warfare" cuts both ways - since detector-detectors use a similar superheterodyne receiver, many early "stealth" radar detectors were equipped with a radar-detector-detector-detector circuit, which shuts down the main radar receiver when the detector-detector's signal is sensed, thus preventing detection by such equipment. This technique borrows from ELINT surveillance countermeasures. In the early 1990s, BEL-Tronics, Inc. of Ontario, Canada (where radar detector use is prohibited in most provinces) found that the local oscillator frequency of the detector could be altered to be out of the range of the VG-2 Interceptor. This resulted in detector manufacturers responding by changing their local oscillator frequency. Today, practically every radar detector on the market is immune to the VG-2 Interceptor.. The VG-2 is no longer in production and radar detectors immune to the Spectre Elite are available.

Radar scrambling

It is illegal in many countries to sell or possess any products that actively transmit radar signals intended to jam radar equipment. In the United States, actively transmitting on a frequency licensed by the Federal Communications Commission (FCC) without a licence is a violation of FCC regulations, which may be punishable by fines up to $10,000 and/or up to one year imprisonment.

LIDAR detection

Newer speed detection devices use pulsed laser light, commonly referred to as LIDAR, rather than radio waves. Radar detectors, which detect radio transmissions, are therefore unable to detect the infrared light emitted by LIDAR guns so a different type of device called a LIDAR detector is required. LIDAR detection, however, is not nearly as effective as radar detection because the output beam is very focused. While radar's radio waves can expand to 85 feet (26 m) across at 1,000 feet (300 m) from their source, LIDAR's light beam diffuses to only about 6 feet (1.8 m). Also, a police officer targeting a car will most likely aim for the centre mass or headlight of the vehicle and, because radar detectors are mounted on the windshield away from the beam's aim, they may not alert at all. Lastly, with such a focused beam, an officer using a LIDAR gun can target a single car in close proximity to others at ranges of up to 3,000 feet (910 m). This has resulted in some manufacturers producing LIDAR jammers. Unlike radar, LIDAR's frequencies and use are not controlled by the FCC. These jammers attempt to confuse police LIDAR into showing no speed on the display. Many times they are successful, and therefore many LIDAR manufacturers are producing LIDAR guns that have "jam codes" which show when they are being jammed. They will work on some LIDAR jammers and not others. In spite of this, police can often tell when they are being jammed when they get no reading on their LIDAR. Many jammer-equipped motorists using jammers now try to counter this by reducing their speed to legal limits before they turn their jammer equipment off or "kill the equipment" referred to as "JTK" or "Jam to Kill." Officers can often tell this is going on by just watching for their LIDAR equipment not being able to lock in a speed properly along with visual indication of sudden deceleration of the targeted vehicle. They will then pull the offending vehicle over and look for LIDAR jammers on the front of the vehicle and can hit the motorist with an obstruction of justice charge should they be found. Some states also have laws about any police radar or LIDAR jamming. These are CA, UT, CO, OK, TX, MN, IL, TN, VA, SC. In these states the penalties can be severe.

Despite the advent of LIDAR speed detection, radar remains more prevalent because of its lower price relative to LIDAR equipment and the amount of radar equipment already in service. In addition, in order to use LIDAR the officer must be stationary and cannot be moving at all on account of the need for a very precise aim.

Legality

Using or possessing a radar detector or jammer is illegal in certain countries, and it may result in fines, seizure of the device, or both. These prohibitions generally are introduced under the premise that a driver who uses a radar detector will pose a greater risk of accident than a driver who does not. The table below provides information about laws regarding radar detectors in particular nations. In 1967 devices to warn drivers of radar speed traps were being manufactured in the United Kingdom; they were deemed illegal under the Wireless Telegraphy Act 1949.