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You're saying that PD have a an antennae to detect metallic strips in a dollar bill inside of a metal car.

It wouldn't be just an antennae. It would have to be some radar-like technology that returns a "hit" if encountering a large stack of bills. Not entirely out of the realm of reality, but I'm also not saying that it exists, more musing upon the idea. I mean, I've read about these instances of Civil Asset Forfeiture for about a decade now and the profit motive is a strong one!

Best to you!