Radar Detectors

Detecting Radar | Detectors | Restrictions


Sometimes police transmit constantly, sometimes police only transmit (Instant-on mode) when targeting a vehicle. Detectors work well for constantly transmitting radars, but can leave little time (fractions to several seconds) to react to Instant-on transmissions. A detector will pickup an Instant-on radar targeting a distance vehicle well in front of the detector, but detections are short, seconds, and sporadic if at all. A good detector can pickup a transmitting radar several miles away in an open environment.

Some photo radars are fixed, some are mobile (but operate from a stationary position). All fixed and some mobile photo radars are unattended and transmit constantly. Mobile radars with an operator only transmit when a vehicle is close to the beam (less than 150 feet from the radar). Photo radar angles the beam across-the-road, instead of down-the-road. A detector might pickup a constantly transmitting across-the-road (photo radar or safety radar sign) at about a quarter mile range, but it could be much less.

Note: not all speed camera systems use radar. Some systems use road sensors, some use 2 or more license plate recognition cameras. Detectors will not recognize these systems, unless the detector has a GPS and database of speed camera (some databases include red light camera) sites.

All detectors are subject to false alerts, but some detectors are better than others at recognizing non-radar signals for fewer false alerts. There are numerous transmitters in the X and K bands that can cause a radar detector alert.

Radar Detector False Alert Sources
Application Use
- intended to setoff detectors
- safety radar
- railroad locomotives
- train yards
- sporting events
- homes
- business
- public buildings
Door Openers
- business
- vehicle entrances
- railroad train entrances
- vehicle radar
- moving farm equipment
- specialized railroad cars
- fork lifts

A lidar beam is only 0.2° wide, or about 1 foot in diameter at 100 yards. For comparison, a radar beam that is 12° wide, has a 75 feet diameter spread (fan out) at 100 yards. Police are trained to aim a lidar beam at the most reflective parts of a vehicle such as license plate, front grill, lights, or bumper. In most cases a lidar beam will not hit a detector, making lidar detection highly unreliable. All lidar's are Instant-on only, making detection even more unreliable, and leaving little if any reaction time.

The chances of detecting a signal is;

Some detectors mount to the front windshield with suction cups, some attach to a sun visor. The detector should have a clear field-of-view to the road. Keep the detector clear of wiper blades, toll / bridge transponders, window stickers, and other objects. Some windshields have tinting on the edges that can interfere with detector reception. Detectors with rear and/or side coverage should have a clear view of the rear and/or side. On some vehicles the side and rear windows are tinted with a metallic film that can reduce detector reception.

To get the best radar reception the detector should be mounted as high as possible. To get (higher chance to get) the best lidar reception the detector should be mounted low. The chances of getting a lidar signal is remote, additionally if the detector has rear and/or side coverage a higher mount is preferable.


Radar detectors are 2 devices built into one, a microwave receiver and a laser sensor. Detector's use an antenna to capture radar signals, and a separate optical aperture for laser signals.

All detectors have front coverage, some also have rear coverage, and some also have side coverage (360°). Front coverage has better detection than rear coverage, and rear coverage has better detection than side coverage. A few radars with 360° coverage have direction indicators, (front, rear, left, right).

All detectors indicate when a radar or lidar has been detected. Most detectors have a radar signal strength indicator and audio warning beeps, faster beeps for stronger signals. When a lidar is detected an indicator lights up and sounds an audio tone, click, beep, or message, but no signal strength indication.

Rdar Detector Indicators

Radar Detector Indicators

Many detectors indicate the radar band, X, K, or Ka. Some detectors combine X and K band detections into a single indicator (X/K) - an X or a K band radar has been detected. Some detectors combine K and Ka band detections into a single indicator (K/Ka) - a K or a Ka-band radar has been detected.

Radar Detector Spectrum
Band Frequency Notes
X 10.500 - 10.550 GHz Few areas use X band.
Used in IN, NC, NJ, OH
K 24.050 - 24.250 GHz Common
Ka 33.4 - 36.0 GHz Widespread
IR 820 - 950 nm Lidar wavelength

A few radar models by one manufacturer have a POP mode that cannot be picked-up by most detectors. Some detectors can pickup the mode by incorporating additional processing.

The radar transmits a short 0.067 second pulse, too short for many radar detectors to pickup. The pulse is also too short for the radar to get a reliable measurement, only a speed estimate. The officer must switch to normal mode to get a real speed reading, according to the manufacturer.

In POP mode the radar transmitter is still warming up, making speed measurements outright wrong and random, and subject to mis-interpretation . The mode is used as a selling point, but is not approved by the International Association of Chiefs of Police (IACP). Only one manufacturer is unscrupulous enough to have some models with a POP mode.

Police use a Radar Detector Detector (RDD) to enforce radar detector restrictions (see below). All radar detectors leak internal signals, an RDD is designed to pickup this leakage. Most RDD's are about the size of a radar detector, some are larger. RDD's are used in the same manner as a radar detector, point the antenna in the direction of interest.

RDD Types (Models)
- Stalcar / Spectre (more / less...)
- MD-3, RD-1, RD-2, RD-3 (more / less...)
- VG-2 Interceptor (more / less...)

Some radar detectors can pickup some RDD models. Most detectors shut down automatically when and while an RDD is detected.

A very few places and vehicles broadcast safety signals that some radar detectors can receive. A safety signal alerts drivers of a hazard in the area and might be found in construction zones, highways, and emergency or oversized vehicles.There are not enough safety transmitters for this to be a major consideration, if a consideration at all, when purchasing a radar detector. A number of high performance radar detectors don't waste processing time looking for or decoding these signals.

SAFETY TRANSMITTERS (more / less...)

Many radar detectors can detect an emergency vehicle's strobe light. Some emergency vehicles use a strobe light when the emergency lights are activated. The strobe changes (is suppose to) traffic lights (with strobe detectors) to green. Sometimes it works, and sometimes is doesn't. In most situations a strobe will not illuminate a detector's optical aperture, and not trigger an alert.

Some radar detectors have a built-in GPS and a red light / speed camera database of fixed (permanent) locations. The GPS portion of the detector will alert a driver when approaching a location in the database. The database should be updated regularly, as red light and speed camera locations come and go. Many dedicated GPS's (no radar detection capabilities) can be loaded with a speed and red light camera database to alert drivers when approaching a ticket camera.

The database will not contain mobile photo radars. These radars are mounted in vans or cars, or on a trailer, or come in a tripod configuration, and can be easily moved and setup. However, a detector's microwave receiver should pickup photo radar.

Some detectors with a GPS, and most dedicated GPS's, allow the user to program custom locations to sound an alert for places of interest such as speed traps, false alert areas, etc.


- X/K, Ka, Lidar
- VG-26, SA5
- X, K, Ka, POP, Lidar
- Signal Direction, VG2
GPS/Camera Database
- X, K, Ka, POP, Lidar
- Signal Direction
High Performance
  1. can disable one or more radar bands.
  2. can be programmed for Ku and other frequencies.
  3. 360° coverage.
  4. auto shutdown when and while RDD detected.
  5. does not decode safety message.
  6. invisible to VG-2.


Radar detectors are legal in the US except in Virginia, Washington DC, military installations, vehicles over 10,000 pounds, and commercial vehicles. Detectors are also illegal in some provinces in Canada and some states in Australia.

Radar Detectors are ILLEGAL in:
  • Virginia
  • District of Columbia
  • Military Installations
  • Vehicles over 10,000 pounds
  • Commercial Vehicles

Some states (for example Minnesota and California, probably more) limit what can and cannot be placed and/or used on windshields. Alternatives include sun visor or dashboard mounting.

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Radar Detectors
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