Parked in the middle of a busy street, Maplewood police officer Steve Hiebert's squad car was busy, too -- three small cameras mounted on the trunk were rapidly snapping photos of passing license plates.

A wide shot of vehicles' rear views flashed across a laptop in Hiebert's car as a beep similar to that of a grocery checkout scanner sounded. A detailed picture of the plates also appeared on the screen.

It's all part of Maplewood's new automatic license plate reader (ALPR) system, designed to catch stolen or scofflaw vehicles -- cars registered to owners with suspended licenses, unpaid fines or serious infractions such as DWIs.

Alarms unique to each offense sound whenever the system scans a plate registered in the Minnesota Bureau of Criminal Apprehension's database of stolen and scofflaw vehicles. A computerized voice identifies the infraction.

"I'm sure you're going to see more and more of them, because they're so effective," said Police Chief Dave Thomalla, adding that the Maplewood department is already looking into acquiring a second unit. He said the camera photographs only reflective surfaces at low heights, so citizens needn't worry about their faces being photographed.

The system was installed this month. Previously, Hiebert, the sole officer assigned purely to traffic enforcement, patrolled the city, entering license plate numbers by hand at random.

"I call it fishing," Hiebert said. The new camera allows him to work more efficiently.

There were 189 stolen cars recovered in Maplewood last year, up from 176 in 2009.

St. Paul police installed two of the units about six months ago, and now have a total of seven. Since the department began using them in 2008, officers have recovered 631 stolen cars and caught 1,051 scofflaw vehicles.

Intrigued by Maplewood's success (Hiebert caught a stolen car as it drove past him two days after the camera became operational), Roseville police are considering one, said Roseville police Lt. Lorne Rosand.

St. Paul and Maplewood got their units, at more than $20,000 each, through a state grant for auto theft prevention.

The unit has its quirks, too. When the alarm sounds, Hiebert still has to double-check the plates by manually entering the plate numbers into his laptop, which accesses an up-to-the-minute database. (The ALPR's database is updated twice a day.) Hiebert then waits to verify the camera's results. The unit also sounds an alarm if a Minnesota plate matches plates of a car stolen from another state, and takes several seconds to note this on the computer screen.

On a recent afternoon, Hiebert caught several drivers who shouldn't have been on the road. The camera also photographed a nearby light post.

Chao Xiong • 612-270-4708 Follow Chao on Twitter: @ChaoStrib