I agree with MLS515, but I still use the Valentine One, and I think it is remarkably good. If (as MLS notes) the first radar your detector.. well, detects is when the constable "paints" you after he makes visual contact, then the radar detector will be very effective at confirming that you are about to be written up for a speeding citation.
But a good radar detector will notify you that radar is being used (aginst other drivers ahead of you) in plenty of time- mine often receives radar at distances of two or more miles.
Noting from your profile that you are in Austria, I presume that radar detectors are illegal there. If that's the case, well, you cannot reasonably use a windshield-mounted one without risk; but you could use a Valentine One, mounted in a well-designed console of some sort between your rear-view mirror and the car's roof, with some sort of disguies over its front (nothing that would block microwave radiation ,of course!). Then, you'd use the reote display module that can be purchased for the V-1, mount it inconspicuously on the dashboard somewhere, and you're rocking and rolling.
...three miles from BRONS, clear for the ILS one five approach...