redneck radar
n.— «We made it up north this weekend in record time, thanks to what my brother and his friends call redneck radar, i.e. relying on the even faster drivers ahead of you to reveal where police are located.» —“You might say redneck if…“ by Dan Language is the People’s (St. Paul, Minnesota) Nov. 5, 2007. (source: Double-Tongued Dictionary)
Further reading
If you speak a second or third language, you may remember the first time you dreamed in that new tongue. But does this milestone mean you’re actually fluent? And a couple’s dispute over the word regret: Say you wish you’d been able...
I tried to find other uses of this term (in this sense) before I posted about it, but the closest I came was a 2004 post in the “Banshee HQ Forums.” Responding to the question “Fastest u ever went on land,” one user commented “78-80 (not sure… used redneck radar, a.k.a. vehicle beside you).” Eh…