Oh my, not radar detectors again!
Ok, for those of you that swear by them, good for you. For those of you that have gotten citations while using one, I'm sure you're swearing at them. A few basic facts about radar that might help you decide wether they're worth it or not.
Today's modern radar devices in use by LEO's have a stand by mode. That means they're not sending out a signal or wave to be detected. Once the officer identifies a target, he/she visually estimates the speed then pulls the trigger so to speak. At that very instant, they have your speed...at the speed of light, which is 186,000 miles per second. Here in NC we have to be certified to operate Radar and Laser/Lidar. The class is two weeks long and if you can't estimate speed within 3.5 mph of the actual speed then you fail. It isn't easy.
Another very effective speed measuring device is VASCAR (TDI). Basically, a computerized stop watch and time distance measuring instrument. Two white lines 1/8 of a mile apart, the target is timed between those lines and they have your speed. This device sends out nothing to be detected. Please keep this in mind when making an expensive purchase.
All of the detectors on the market will detect radar if it's being transmitted constantly. Where they will fail you is when it's used properly in stand by mode. Oh, dont forget about airborn LEO's using helicopters and VASCAR.

BTW, any device that jams SMI's is illegal.
Hope this helps.