Charles County Sheriff Senior Detective Charles Baker has two tiny cameras on roof of cruiser that automatically scans license plates. The information is processed on a computer. (James A. Parcell/For The Washington Post)

The license plate reader found the Accord’s tags were suspended, which the officer confirmed with state police headquarters. The officer pulled over the driver, Jason Kyle Knight, and discovered that he had an outstanding felony warrant for distributing drugs and obtaining a prescription by fraud in Fairfax County, police said.

The officer arrested Knight, who has addresses listed in Braddock Heights and Bradenton, Fla.. Polcie said Knight was charged with traffic citations and held without bond on a fugitive warrant.

The arrest was a prime example of how the license plate reader systems, which are being employed by a number of local law enforcment agencies, are supposed to work. The systems became popular in Britain in the 1990s as a way to deter Irish Republican Army attacks.

Authorities in the Washington area began installing about 200 license plate readers on cruisers and along roads in 2008. At the time, privacy advocates raised concerns about how the data the systems collect would be used. Officials said they didn’t plan to store data on the scanned license plates, except for those associated with terrorism or other crimes.

A license plate reader also helped lead police to the stolen jeep of slain American University professor Sue Ann Marcum last October.