Speed Camera Technology
Speed cameras and police speed traps can come in various forms using several different technologies to catch people speeding. To match these measures, camera detectors are also available using one or more technologies to defend your licence from getting points for speeding. The technologies are radar, laser and digital cameras, which can be alerted to via a GPS-based detector.
Radar Detectors
Radar technology is used by the infamous Gatso camera, and so radar detectors became the first technology available to give alerts to these Gatso speed cameras. We still talk about radar detectors today as a generic term to mean a speed camera detector, although they do not always actually detect by radar these days.
Radar is effectively a radio wave and the Gatso cameras emit this signal which is distorted by passing traffic. Depending on the speed of the traffic and the level or distortion, a speeding vehicle would trigger the camera. A radar detector receives the return signal much in the same way that a car stereo would receive a radio wave from a radio station, the only difference being that the strength of signal being given off by a Gatso camera is very low and more sensitive technology is needed to detect this frequency. As you're driving down the road and approaching a Gatso camera, your radar detector would tune into its frequency and gives an alert so you are forewarned about the radar emitting equipment in the immediate vicinity.
Laser Detectors
Laser works in a similar fashion, except that it is a light wave involved, and unlike radar, laser is not constantly emitted and does not hang around in the air. Most radar detectors will also detect laser frequencies. Laser is a newer technology for the police and has superseded the use of radar in police handheld speed guns. It is these laser guns which are used in the mobile safety camera vans you often see parked up at the side of the road or on bridges over motorways with the back doors or side windows open.
GPS-based Detector
More recently the police have added a whole range of speed trap cameras to their arsenal, and one of these is the Truvelo camera, standing for True Velocity. This camera has sensor strips built into the road to determine your speed, and the camera is forward facing so it can catch you before you pass, and additionally identifies the driver of the car.
Another digital camera system is called SPECS developed by Speed Check Services. This system uses a set of two or more CCTV-based cameras that are capable of reading number plates. As you pass each of the two or more cameras, the time that your number plate was read at each location is calculated against the distance between the cameras, and if your average speed is quicker than the speed limit would allow you to travel between the locations then a ticket is automatically issued.
As these varieties of cameras do not emit any signals, their locations cannot be identified by frequency detection models. Instead, a GPS system can be loaded with the latitude and longitude co-ordinates of all the camera locations, and then much like a satellite navigation system it can compare your location against this database as you drive and warn you accordingly.