Which speed detection device relies on the Doppler effect?

The speed detection device that relies on the Doppler effect is radar. The Doppler effect refers to the change in frequency or wavelength of a wave in relation to an observer moving relative to the wave source. In the context of radar speed detection, the device emits radio waves that bounce off moving vehicles. When these waves return, the frequency changes based on the speed of the vehicle moving towards or away from the radar unit. The radar device measures this frequency change to calculate the speed of the vehicle.

Radar is widely used in law enforcement for speed enforcement as it provides quick and accurate readings of a vehicle's speed from a distance. This capability makes it an effective tool for tracking speeding vehicles on highways and roads.

The other devices mentioned work differently: Lidar uses laser technology to measure distance and speed based on the time it takes for a laser beam to hit an object and reflect back. GPS relies on satellite signals to determine position and speed but does not utilize the Doppler effect. Camera systems typically capture images of vehicles and may incorporate additional technology for speed detection, but they do not specifically use the Doppler effect for calculating speed.