How do the police know how fast you are going, anyway? California
police officers have several different types of technology at their
disposal to enable them to catch speeders. Radar is the most common.
Radar devices can be either mounted in a police car or portable "radar
guns." The police do not have to aim the radar at a specific vehicle to
get a reading-the radar will pick up all the vehicles on a given
stretch of road. Basically, radar devices send out an electromagnetic
signal that bounces off of your car. The signal bounces back to the
radar device after it hits your vehicle-but due to the Doppler Effect,
it comes back at a different frequency. The return frequency depends on
how fast your vehicle was going, enabling the police to calculate your
You can buy radar detectors that pick up radar signals and let you know
when it's time to slow down, although there's always a risk that the
device won't warn you in time. However, laser devices known as LIDAR
help police measure your speed without setting off your radar detector.
LIDAR devices work by aiming a beam of laser light at your vehicle and
measuring the amount of time it takes for the laser beam to be
reflected back. They are not available as portable "guns", and they
have to be aimed at a specific car to get a reading. However, they are
accurate and undetectable to traditional radar detectors. LIDAR
detectors are available, but by the time the laser sets them off, the
cop already has you in his sights and it’s too late to avoid a
California speeding citation.
Aircraft is sometimes used to spot speeders in California. In most
states, aircraft catch speeders by measuring the amount of time it
takes a vehicle to travel a known distance. However, this method of
measuring speed, known as VASCAR, is illegal in California. In
California, aircraft can be used to spot speeders, but officers on the
ground must use radar or LIDAR to get a reading of your speed before
they can stop you.