Laser and radar guns are similar in appearance although they operate on very different principles. Laser means Light Amplification by Stimulated Emission of Radiation.Laser cannot detect speed from the side of a vehicle. Like radar, laser guns are line of sight systems that require a reflective source in front of them from which to bounce a signal.Transmitting on 904 nanometers and traveling at 186,000 miles per second, laser guns utilize a very tight, invisible beam of light to target moving vehicles. To work properly, laser gun manufacturers typically recommend a maximum angle of 10 degrees off center of the target. Essentially, this is a straight shot to the front or rear of the moving target. Police are trained to aim for a low, reflective source in front of the car, like a license plate, or head light.Police use of laser guns is rapidly increasing. Over 30,000 guns are operational throughout North America. According to R.A.D.A.R., a non-profit organization dedicated to protecting the constitutional rights of radar detector owners, 47 out of 50 states in the U.S. have access to laser guns.The use of laser guns is most prevalent in areas with higher traffic concentration and larger tax budgets that enable police department spending on the latest technology.To increase laser usage of laser guns, manufacturers often provide police departments with laser guns to use and charge them after enough tickets have been issued to pay for them. As a result, drivers are often surprised to encounter police laser in areas not expected to have access to this more expensive technology.Each emitted pulse is timed leaving the laser gun and again when it returns. The difference is displayed as miles per hour.Laser & Radar guns are different. While laser guns do have a few disadvantages to their radar counterpart (they are more expensive, they can not be used from a moving vehicle or behind glass, and they must be held extremely steady while targeting), they do have some very compelling benefits for police. The advantage of laser is it's very narrow beam which allows police to clock individual cars, even when surrounded by other vehicles. At typical target ranges of less than 1000 feet, the diameter of a laser beam is less than three feet. A radar beam, with its wide scattering microwave signals, can be 250 feet in diameter at 1000 feet, large enough to cover all lanes of traffic on a busy highway and nearly impossible to pinpoint a single vehicle.Effective Countermeasures - As more and more police departments add laser guns to their arsenal of speed measurement devices, one thing is clear - by the time ordinary detectors give you a warning, it's TOO LATE.The only way to effectively combat a laser gun is with an active device in front of your car, where police aim. http://www.superiorcarcare.net/policelaser.html Echo and Doppler Shift When you shout into a well, the sound of your shout travels down the well and is reflected (echoes) off the surface of the water at the bottom of the well.