Police have long used radars to track the speed of drivers and
to help maintain safe roads. Meanwhile, many drivers have begun
using radar detectors to help avoid costly fines for speeding
violations. Despite the popularity of radars and radar
detectors, many people do not understand the science or
technology behind them.
Police radar guns work by transmitting radio waves from the
radar to the target vehicle and back. Because radio waves move
through the air at a constant speed (the speed of light), radars
can calculate how far away an object is based upon how long it
takes to the radio signal to return. When an object such as a
vehicle is moving, there is a change in frequency in the radio
waves. Radars detect this change and convert it into miles per
hour to determine the target's speed. Further, radar guns also
use different types of bands to determine the target's speed,
including X band, K band, and Ka band. Traditional radar
detectors alert the driver to the presence of radars.
Law enforcement officers also use lasers (concentrated light) to
determine a vehicle's speed. Laser radar guns measure the time
it takes for infrared light to leave its origin, reach a car,
bounce off, and return. These tools can determine how far away
an object is by multiplying this time by the speed of light.
Because this type of radar sends out many bursts of light to
determine multiple distances, the system can determine how fast
the car is moving by comparing these samples. However, because
laser speed detectors have a much more focused beam and detect
lasers over great distances, police laser guns are generally
more difficult to evade. While modern radar detectors often
include a light-sensitive panel that detects these light beams,
the detector (and thus vehicle) is usually already in the beam's
sights.
While traditional detectors worked by alerting the driver to the
presence of the radar or laser, the last few years have seen a
rise in radars that also emit a jamming signal. This signal
duplicates the original signal from the police radar gun and
mixes it with additional radio noise, which confuses the radar
receiver, and prevents the police officer from preventing an
accurate speed reading. Some detectors also use a laser jammer,
or light emitting diodes (LEDs), that produce a light beam of
their own. This beam prevents the receiver from recognizing any
reflected light to get a clear reading on the vehicle's speed.
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