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.”