When you get a toll-paying transponder like the E-ZPass, you assume that it just sort of sits there until you drive through a toll booth. That’s not true. Maybe, according to a recent presentation at DEFCON, you should put your E-ZPass away unless you’re actually paying a toll right now.

Toll transponders usually come with a little foil pouch. You’re to use this when you don’t want the tollbooth to pick up your signal: say, when a friend is paying tolls in cash for you or when you’re cheating on your partner with someone a few highway exits away and don’t want to leave a record of your whereabouts. (Note: the latter use is not endorsed by the E-ZPass Inter-agency Group.)

Forbes reports that one electronics tinkerer, Puking Monkey, became justifiably obsessed with different ways that the authorities might be tracking drivers while we go about our business. He wondered whether his E-ZPass was ever being read outside of a tollbooth, so he did the obvious thing and hacked it to light up and moo when it it was read.

Here it is on a trip in midtown Manhattan:

What the heck? It turns out that the city of New York was reading the tags…but not to hunt for wanted criminals. According to the company that made the tag readers, it’s part of a traffic-control system meant to replace sensors below the pavement.

“Instead of conventional, in-pavement inductive loops that degrade with wear and age, this system uses roadside or overhead microwave sensors, E-ZPass RFID readers, and video cameras,” explains Transcore. The identities of the drivers are supposedly masked, so there’s no comprehensive record of drivers’ movements through the city. The thing is, though, there’s nothing about this in the Terms & Conditions when driver signs up for an E-ZPass.

Is this happening only in New York City? The tell-tale moocow is now on a road trip through other states to find out.

E-ZPasses Get Read All Over New York (Not Just At Toll Booths) [Forbes]

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