Geektastic: The purpose of speed traps is to encourage safer driving. Ergo, having a detector remind you you're speeding or that there is a fixed camera is likely to cause you to slow down if you were in need of doing so. Road safety aim achieved.
Ideally speed cameras and policemen would never catch anyone because we'd all be sensible enough and skilled enough not to speed.
Allowing people to have tools that help moderate their behaviour is IMV sensible.
I don't disagree, but every car is equipped with a 'tool'...it's called a speedometer. Now if there was only an invention that allowed the driver to alert others when they were intending to make a turn, that would be very helpful.