A lot of departments are switching to lidar. (light interigator blah blah blah, could be way off on that, but it uses light). Radar detectors are worthless to these, its a focused beam so when your detector picks it up, its too late. You're screwed. If I remember right airborne weather radar and police radio based radar both can operate on the x-band frequencies.
Pretty much there's only one radar detector worth anything and that's the valentine one. 300 bucks for that guy. It tells you direction and how many signals its picking up. Which is ideal for using intown. Most of the time in town you're only picking up the radar from automatic doors from the stores and whatnot you're driving by.