The NSA isn’t the only government agency raising concerns about electronic privacy. Local police departments are coming under similar scrutiny – not only for using spying technology, but for hiding their use from the public.

At least 25 police departments now use what is known as "Stingray," a briefcase-sized box that swallows up cell phone data within a mile radius.

More than one in three large police departments are also using license-plate readers, which can record every plate -- even on a four-lane highway – from vehicles going at speeds of up to 150 miles per hour.

The technology is a remarkable crime-fighting tool, according to former D.C. homicide detective Rod Wheeler.

"Not just automobile thefts, but homicides, all kinds of robberies, so the technology is definitely something that's an asset to us," he said.

But in a May 1 article, Wired magazine reported that Harris Corporation, maker of the Stingray, and Vigilant Solutions, which sells license-plate readers, holds its police department buyers to vows of secrecy.

It reported that Vigilant's terms of service says: "This prohibition is specifically intended to prohibit users from cooperating with any media outlet.”

Lon Anderson, with AAA, raised concerns about this provision.

"It's very worrisome,” he said. “I think we want police agencies to be as transparent as possible. There shouldn't be anything to hide here."

He added: "They are using technology that are supported widely because of their proven ability to reduce crime."

Vigilant today told Fox News that its confidentiality policy has changed and that the Wired article was outdated. It said that buyers only need to "check" with Vigilant now before they discuss the technology with the media.

It added in a statement: "This is a common practice in the area of law enforcement technology, since criminals often manipulate publicly available information to avoid detection and capture."

But the two technologies raise broader questions about 4th Amendment protections. Last year, then-Virginia Attorney General Ken Cuccinelli issued an opinion on license-plate readers that said data cannot be collected unless directly related to a criminal case.

The opinion was not binding. Many jurisdictions in Virginia and beyond still retain the data for years.

The last major legislation governing electronic privacy was passed in 1986, before these technologies existed. Courts have ruled differently regarding their use. Settled law is difficult to arrive at, as technological change is turning faster than the wheels of justice.