Useful warning for what, knowing you're speeding?
sh*t, in the 12 years I've been driving I'm sitting on two speeding tickets. One when I was a teenager doing stupid things in his turbo DC2R, and the other from driving when tired and angry, through a speed camera I knew was there.
I'm no advocate for the speed kills crap, but dont pretend there is any reason other than bad driving (speeding) to use a radar detector.