Surveillance experts are raising questions after Walmart patented a surveillance system that could spy on cashiers and customers by collecting audio data.

CBS News reports Walmart's patent filing says the "sound sensors" would focus on minute details of the shopping and checkout experience, such as the beeps of item scanners and the rustling of bags, and they could also pick up conversations of workers and customers.

It's unclear how that chatter could be used.

"This is a very bad idea," Sam Lester, consumer privacy counsel of the Electronic Privacy Information Center in Washington, D.C., told CBS News. "If they do decide to implement this technology, the first thing we would want and expect is to know which privacy expectations are in place."

For more, read CBS News' report.