Yeah,
Check Rocky Mountain Radar out if you want to buy an empty plastic box and an empty promise. See my previous post.
If you want something that works, buy a Valentine one and one of these:
http://www.radar-guys.com/bel/bel904.htm They will cover you on secondary roads and highways (where forward facing radar is the order of the day) and around town (where motorcycle cops shoot with hand held radar or laser).
They will not help much on California freeways, though. Here, the officer will follow you and record your speed with a calibrated speedometer. The only defense here is 20/15 vision and a mirror that doesn't vibrate too much.
Paul