The Daily—Rupert Murdoch's now-defunct iPad news site—says it obtained documents showing that "government officials are quietly installing sophisticated audio surveillance systems on public buses." Athens is among the seven cities with microphones on buses.

Linked to video cameras already in wide use, the microphones will offer a formidable new tool for security and law enforcement. With the new systems, experts say, transit officials can effectively send an invisible police officer to transcribe the individual conversations of every passenger riding on a public bus.

But the deployment of the technology on buses raises urgent questions about the boundaries of legally protected privacy in public spaces, experts say, as transit officials — and perhaps law enforcement agencies given access to the systems — seem positioned to monitor audio communications without search warrants or court supervision.

“This is very shocking,” said Anita Allen, a privacy law expert at the University of Pennsylvania. “It’s a little beyond what we’re accustomed to. The adding of the audio seems more sensitive.”

It all sounds so Big Brother-ish, right? Athens Transit Director Butch McDuffie scoffs. "It's our video and audio surveillance system we've had on our buses for five years," he says. "This article made it sound like it was all hush, hush. No, it's not."

Since the Daily's story started making the rounds on the Internet earlier this week, McDuffie says he's been contacted by CNN, the Today Show and Forbes magazine, and he's had to set them straight. Athens Transit announced it was installing the microphones in 2007, McDuffie said. Signs in English and Spanish alerting people to their presence are posted in buses.

The audio system writes over recordings every 10 to 14 days, and there's no way to eavesdrop on conversations in ordinary time, according to McDuffie. In fact, unless someone is shouting or standing near the driver, engine noise covers up normal conversations, he says. And officials don't have the time, the manpower or the desire to listen to the 3,000 hours of recordings the system makes every day. The surveillance system is mainly used to catch passengers who verbally abuse drivers or other passengers and inappropriate behavior by drivers, and to stop frivolous lawsuits. McDuffie recalls a man who claimed to have injured his back when a Toyota rear-ended a bus.

The system caught him walking around talking to other passengers after the wreck, and the man's lawyer dropped the case, McDuffie says. Another time, a microphone picked up a woman who was trying to board a bus without paying threaten to kill the driver, he says.

"This is to protect the taxpayers," he says.