| Save your money and just be careful. I just recently got a speeding ticket in my MINI and I have done research on radar detectors because of it. For starters there are several different frequencies that police can use, and a detector (especially a cheap one) can’t sense all of them.
Also, some police radar have a switch that only generates a signal when they see you approaching, in which case nothing is being transmitted and your detector has nothing to detect.
Then you have LIDAR, which is used by some pigs (I mean cops). This uses laser light to track your speed, thus there is again no signal for your detector to detect.
And finally, even if you have a detector and do detect a signal, you may already be too late because newer radar guns transmit a signal at very low power and by the time you detect it you are basically caught.
I say just keep an eye out for cops and don’t speed past underpasses or in areas where cops are likely to hide. If you buy a radar detector and end up getting caught speeding anyway what’s the point? …And trust me, once you get nailed once you will slow down and be more careful in the future.  | 
