Radar detectors won't save you if you are the only car on a stretch of road unless the radar gets an invalid return the first time.
Like many above have stated, the detector will only work if you use common sense, and blend in with the traffic around you (move to the right lane as soon as done passing, etc...).
Police are trained to pulse their radars these days and target smaller groups of cars. They wont just leave them on if they are actually out to write tickets. They will also use the terrain to their advantage by parking in blind approaches, on onramps, at the crest of hills with valleys between, where you will get hit with the radar as soon as you crest your hill making it easier to know which car the radar hit and give you much less time to react.
The only time they will keep the radar on is when they are doing preventive and overt type posts, in which they are meant to be seen, and your radars are meant to pick them up.
So detectors can help warn you that other cars (and yours) have just been hit, giving you enough time to slow down and blend in before the officer can figure out which car he wants to target.
Lasers are tougher for obvious reasons (they are aimed specifically at you).
And nothing will save you from the trooper in the air plane above with his stop watches. Just slow down when you see the white hashes spaced 100m or so apart, because that's how they are measuring your speed.
I have a Passport 8500 and I would guess it's saved me from at least 6 or 7 tickets, but I've also had two since I started using it (both times I was the only car in view).
I've been hit with the laser several times, but to be honest, never while speeding so I'm not sure if I would have gotten away with anything or not.
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