Same with radar detectors. You'll be less vulnerable – but you won't be able invulnerable.

Probably the greatest threat – the one radar detectors are least able to protect you from – is so-called "instant- on" radar. The problem isn't that your detector won't detect that you've been targeted. The problem is not detecting the radar in time to do much about it.

Here's how it works:

Revenue collector parks on the shoulder or some other such place where – ideally, from his point of view – he can see oncoming cars before they can see him. He waits, finger on the proverbial trigger. His radar gun's trigger. When he sees you coming, he pulls the trigger and a brief burst of radar emanates from his gun. Just as your radar detector detects the signal, it's already bounced back to him, giving up your speed. You hit the brakes, but it's too late.

He's got you.