In the northeast U.S., most of the tolls people encounter when driving make use of a system called E-ZPass to let them pay the tolls electronically. Drivers are given small RFID transponders that are scanned in tollbooths, at which point the toll is automatically deducted from a pre-paid account. One hacker got curious whether the RFID tags were being scanned elsewhere, so he tweaked his E-ZPass to blink a light and make a noise every time it was read. He tested the streets of New York City, and wasn't surprised to see it light up in plenty of places where there were no tollbooths to be found. From the article: "It’s part of Midtown in Motion, an initiative to feed information from lots of sensors into New York’s traffic management center. A spokesperson for the New York Department of Transportation, Scott Gastel, says the E-Z Pass readers are on highways across the city, and on streets in Manhattan, Brooklyn and Staten Island, and have been in use for years. The city uses the data from the readers to provide real-time traffic information, as for this tool. The DoT was not forthcoming about what exactly was read from the passes or how long geolocation information from the passes was kept. Notably, the fact that E-ZPasses will be used as a tracking device outside of toll payment, is not disclosed anywhere that I could see in the terms and conditions. When I talked to the E-ZPass Inter-agency Group — the umbrella association that oversees the use of the pay-toll-paying tags in 15 different states — it said New York is the only state that is employing this inventive re-use of the tags. ... 'If NYDOT can put up readers, says [the hacker], 'other agencies could as well.'"