A police radar gun operates by transmitting radio waves at certain frequencies which reflects off objects (your vehicle) and are then picked up by the radar gun's receiving section. When radar waves reflect off a moving target, a measurable frequency shift occurs. The radar unit converts this shift into miles per hour to determine the target's speed.

Two basic types of radar are used - stationary and moving. Stationary radar must be used from a  static site, typically a patrol car parked along side the road (See above figure). But with a single antenna moving radar, an officer can clock approaching vehicles while driving on patrol. Moving radar with two antennae - one facing forward, the other aimed out the back of the cruiser - can also clock vehicles even after they have passed by, headed in the opposite direction.

A detector is a radio receiver tuned to specific frequencies used by police radar. It is extremely sensitive, often able to hear radar from over a mile away, far beyond the range at which radar can clock a vehicle's speed. In evaluating a detector, the two most important performance criteria are sensitivity and selectivity. Sensitivity is a measure of a units detection range. Selectivity refers to a unit's ability to reject non-police microwave signals and is an important feature because of the many sources of "electronic pollution". Note: Automatic door openers and some burglar alarms operate on X-band, which is a police band. A radar detector cannot tell if a store is opening a door or a police officer is checking speed.

A detector can alert you of a police presence only when they are transmitting a signal. The officer may have a radar or laser gun in the car but the device may not of been turned on. No detector can alert you if no signal is transmitted!

Early detectors needed only to listen for X band radar. When K band arrived, dual band models able to receive both frequencies (X and K) were required. The introduction of Ka band photo radar (34.3 GHz) led to the development of triband models able to detect X, K, plus a small portion of Ka band. A fourth category of radar receivers called wideband, with X, K and "wideband" Ka (34.2 - 35.2 GHz) detection capabilities reached the market following the introduction of Stalker radar. And finally, in response to the BEE 36A a new generation of radar detectors were developed termed superwideband, which cover all radar guns operating on X, K or "superwideband" Ka (33.2- 36.0 GHz).

When radar detectors proved easily capable of sniffing out radar from miles away, radar gun manufactures responded by producing instant-on radar. In the instant-on mode, the radar's transmitter is placed on hold, ready to fire but not yet producing a signal for detectors to hear. The officer waits until his target is very close (brings a new meaning to "wait till you see the whites of their eyes") releases the radar from stand by mode and gets a speed reading within a second or so. In this situation, no detector offers much warning.
TIP - When traveling in unfamiliar highways always try to find a vehicle which is traveling at the same rate or faster than you are and keep several car lengths behind them. This way the other vehicle can "flush out the radar".

Laser speed guns transmit short bursts of invisible light which bounce off a target vehicle and return to the laser gun. By timing the outgoing and return trips of the light bursts, it can compute the target's speed. The laser's biggest selling point is its narrow beam-only about three feet wide at a distance of 1,000 feet-a feature that provides nearly foolproof target identification. (In comparison, a radar's beam is about 250 feet wide at 1,000 feet.) Laser guns must be used from stationary position and are most effective at short range, usually when targeting traffic at 700 to 1,200 feet.

Since laser guns use a specific light frequency, or wavelength, it is possible to detect a laser's signature light pulse rates. Different laser guns operate at different light pulse rates. Some competitors call them "bands". All Whistler radar/laser detectors receive all current laser guns in use, these include;

• Pro Laser^TM I, II and III
  
• LTI 20-20
  
• Ultra Lyte
  
• Stalker LZ-1
  
• Laser Atlanta L-1
  

A Radar Detector Detector (RDD) is a microwave receiver used by police to detect signals radiated by the local oscillator (A circuit inside the detector) of a radar detector. The trade name of the commonly used RDD manufactured is Interceptor VG-2, most often simply referred to as VG-2. An officer using a VG-2 typically parks next to a busy freeway and aims the device at a 45 degree angle across the traffic stream. The VG-2 acts just like a radar detector when it hears an approaching radar detector, increasing its audio alert rate and progressively lighting more LED's in its visual display. By observing the traffic and watching how the VG-2 responds, the officer can make an educated guess as to which vehicle is using a radar detector. Some detectors are "noisier" than others and can be detected by the VG-2 from as far away as 4,000 feet.

In Virginia, the largest user of the VG-2, officers are not empowered to search a vehicle unless visible signs are present to support the RDD's guess that a radar detector is in the targeted vehicle. Important: A missing cigarette lighter plug, dangling power cord, Velcro on the dash, a mounting bracket on the windshield or visor will tip the officer as to the possible presence of a detector and allow him to search for it. If found, the detector isn't confiscated; the officer notes its serial number, checks to see if it's operational, then hands it back to the driver- along with a citation for having used it.