"I have never understood why it is legal for people to buy gadgets that detect speed cameras.  When they first came out more than a decade ago it was the wealthy with fast cars who bought them, no doubt so they could speed knowing that they will get a warning sound when a speed camera is coming up.  Speeding is dangerous, and I don't see much evidence that it is taken seriously when it is legal to buy a warning system - I gather some sat navs have them now."

Speed cameras are introduced in places that are known to be accident black spots, there has to be a history of accidents on that stretch of road in order for a camera to be put in place. The purpose of those cameras is to encourage people to slow down in those areas. Devices that identify where cameras are positioned lead to drivers slowing down in those areas and therefore Mission Accomplished!