Check out radardetector.net.... enthusiasts and you'll find out all you need! There are a few main choices

For windshield mounts the best are considered:

Valentine 1, Escort Redline, and Escort 9500ix. (V1 is great detector, Redline is awesome - pure performance, and the 9500ix is a great detector with GPS and a few slight drawbacks but is more quieter)

They do work, but ONLY for Radar. Laser is a whole nother ballpark and you will need a laser Jammer if your state does not ban them (they don't in Michigan!)

Do plenty of research! If you are going to get a radar detector get a good one, (do NOT get a Cobra), and get a laser jammer. Laser has little/NO scatter and if your detector detects "laser", you were the target and the police has ALREADY gotten your speed.