Before you purchase a radar detector, it's important to understand the different kinds of radar used by the police. Police radar guns work by emitting a microwave pulse to measure the speed of a moving vehicle; radar detectors work by sending out a signal that mixes with this pulse to produce a lower, more easily detected frequency.
X-band radar (10.5 to 10.55 GHz) used to be the most popular gun used, but it is now all but obsolete. X-band is also the frequency that causes the most false alarms. That's because many supermarket automatic doors, garage-door openers and motion detectors run on the same frequency. More expensive radar detectors have a city mode that lets you downgrade or disable a detector's sensitivity to X-band, thereby cutting down on the number of false alarms from sources other than law enforcement.
The majority of radar guns operate on the K-band (24.05 to 24.25 GHz) or Ka-band (33.4 to 36 GHz) frequency. K-band and Ka-band guns are especially tricky because they can be turned on instantly. If an officer chooses your car, it's almost impossible to be warned ahead of time. However, good detectors can provide a warning if a radar gun is targeting vehicles ahead of yours, giving you enough time to slow down.
Law enforcement has found a new way to stack the deck with POP modes on a few radar guns. POP modes allow officers to send out signals in bursts too short to be picked up by many radar detectors. The catch is that speeders caught using POP modes can't be ticketed because the law requires a radar gun to lock onto a vehicle. However, if law enforcement officers detect a speeding vehicle using POP mode, they can then flip the gun into constant-on mode and get a lock on a vehicle.
POP poses no problem for any radar detector in the latest test at Speed Measurement Laboratories, with every unit detecting K- and Ka-band POP. Still, the testers say POP isn't widely used anyway: Only Oregon, Nevada and Iowa include POP radar guns as a purchasing option under state contract for police. "Do officers use it in the field... seldom, if ever!"
Laser guns are increasingly popular. Police particularly like to use them on crowded roads because laser light beams are so tight, they can easily pick a speeding car out of a crowd. Another positive for police is that, generally speaking, laser guns give off little advance warning, unlike radar, which puts out a relatively broad signal that can be detected miles away. That means that once a laser detector sounds its alert, it's often aimed squarely at you.
Laser guns do have some downsides for police, however. Because the laser must reflect back to the gun off a flat surface, the police have to get a good aim, usually at your front or back license plate or headlights. In addition, laser guns have to be used from a stationary position, giving you some opportunity to visually spot the speed trap. And if the officer turns on the laser gun too soon, a laser detector may give you enough warning that you can slow down before you get within ticketing range.
Radar detectors in Speed Measurement Laboratories' most recent test usually detected laser at 1,500 feet on flat terrain, possibly giving the driver a little time to slow down. However, although a New Jersey judge ruled in 1996 that laser guns can't target vehicles from more than 1,000 feet away because the beam could actually hit a different car, GuysofLidar.com says police still write tickets from farther away.
Most radar detectors can also detect laser guns, but experts say a laser detector alone is of limited use. Instead, they recommend coupling the detector with a laser jammer (which, unlike radar jammers, remain legal in most states) or another countermeasure such as an anti-reflective coating on your headlights or license plates.
Finally, some police departments use a device known as a radar-detector detector (RDD) to alert them to vehicles equipped with radar detectors. For passenger cars, using a radar detector is legal everywhere in the U.S. except Virginia, Washington, D.C. and on military bases. However, they are illegal in big commercial trucks and in much of Canada.
Radar detectors are getting better at covering up their telltale signal leakages, though. In Speed Measurement Laboratories' latest tests, 10 radar detectors prove invisible to at least some RDD models, and three radar detectors outsmarted all of the RDDs: the top-rated Escort RedLine (*Est. $500), the similar Beltronics STi Magnum (*Est. $470) and the pricey custom-installed Beltronics STi-R Plus (*Est. $1,250).
It's also important to realize that no radar detector will report every single radar encounter. There are too many variables, such as terrain, angle of the gun to the car, interference from other traffic, etc. Although certain models do better than others, no radar detector will spot 100 percent of radar threats 100 percent of the time.
Today, the best radar detectors don't simply sniff out police radar guns. They're stuffed with a host of new technologies -- laser detectors, laser jammers, GPS chips that can mark speed traps and red-light cameras -- all to provide blanket protection against speeding tickets. But do you really need all of these expensive features? Here's what experts say to consider when you're shopping for a radar detector: