What is a Radar Detector?

A radar detector in general terms is a device which has the capability to detect or recognise a radar signal.
What does that mean to you, well if you are a motorist then this is quite significant. On UK roads(and in other countries) there are devices known as speedtraps.
Speedtraps are designed to record the speed of vehicles that may be travelling above the local speed limit posted for that road.
The speedtraps can use various forms of speed recording and one of these types of speedtrap is called Gatso and uses radar. The radar is transmitted by the speedtrap which also has a receiver. When the signal is sent out from the speedtrap it will have a particular wavelength. When the signal is reflected back by a vehicle if the vehicle is moving in relation to the transmitter,the wavelength will have changed this is known as Doppler Effect.
The receiver picks up this altered signal and reads it's wavelength, the difference between the transmitted wavelength and received wavelength will give an indication of the speed of the vehicle.
If the speed is above the threshold that the speedtrap has been set to then the speedtrap will initiate the action of a camera which is built into the Gatso speedtrap. The camera will take 2 images in quick succession.
As there are lines painted onto the road surface (equally spaced apart) the 2 pictures can be used as further evidence that the vehicle was speeding, as speed is calculated from distance travelled over time elapsed. e.g. metres per second, kilometres per hour or miles per hour.

If a driver could identify areas where a radar signal is being used then it could help the driver to be reminded to check their speed before they drive into the radar operated speedtrap. A radar detector is usually able to do this and give up to 100 metres warning depending on the quality and sensitivity of the particular detector, the conditions around the Gatso camera and the amount of traffic already going through the speedtrap itself.

Problems with radar detectors are :

  1. False alarms, these occur when a signal similar to a radar signal is being detected and confuse the detector. Radar is a microwave radio signal and there are many devices which use microwave radio signals such as mobile phones, some types of car alarms, automated doors on shops etc. So common false alarms come from these sorts of equipment.
  2. Although Gatso cameras still use radar to detect speed not all speedtraps are Gatso cameras. There are now Truvelo and SPECS and other types which do not use radar and so a radar detector would give no warning of these types of speedtrap and may give the driver a false sense of security.