A speed radar gun works by sending a radio wave from a transmitter that bounces off the moving vehicle and reflects back to the radar gun. Due to the Doppler effect, the frequency of the radio wave reflected from the moving vehicle is different from the first radio wave transmitted from the radar gun. The difference in the two radio wave frequencies is then used by the radar gun to calculate the speed of the moving vehicle.
Car-speed radars come in two other main forms: stationary and moving. Stationary radar determines a vehicle's speed by creating a mixed signal, known as a heterodyne, from the combined transmitted and received radio waves. The frequency of the heterodyne is then measured to calculate the speed of the moving vehicle. Moving radar works by receiving reflected radio waves from the moving vehicle and a stationary object in the background. The moving radar then compares the differences in the two radio waves' frequencies to calculate the speed of the moving vehicle.
A laser speed gun works by transmitting a beam of light to a moving vehicle and measuring the time it takes for it to return. The laser speed gun transmits a very small beam of light, creating a more accurate reading of the surrounding environment for the individual using the device. The disadvantage to this is that the operator must be far more accurate in aiming the device in comparison to using a radar gun that emits a very broad signal.