Moses Cortez grips a device in his hands that looks like a radar gun. From a white Arlington County van, he aims the four-pound contraption at the license plates of parked vehicles.

A badge hanging loosely around his neck, Cortez zigzags across the county's 26-square miles, searching for offenders. In his pressed slacks and shirt, residents might easily mistake him for a plainclothes police officer, but he handles a different kind of law enforcement.

He's the tax man.

Cortez, who works for the county treasurer's office, has new ammunition to help him find residents who have failed to settle their debts, including property tax bills, parking tickets -- even library fines. If they still don't pay up, the county will seize their car.

"It's not like we're sneaking around public thoroughfares," said Arlington Treasurer Francis X. O'Leary. "But you go and you take their tags, and you can imagine their stress. Well, we're pretty upset, too. These people are scofflaws."

The device Cortez is holding is a barrel-shaped camera with a built-in automatic shutter that snaps photos of license plates. The tag numbers then appear on a laptop mounted inside the vehicle and are checked against a database.

Initially created to help police officers capture criminals, the camera has gained popularity among tax collectors. Arlington began using the $27,000 camera last year to locate scofflaws, and Alexandria recently started deploying it for parking enforcement and plans to buy another for tax collection. Other jurisdictions in the Washington region are checking it out.

In New Haven, Conn., where tax collectors and parking enforcement officers have already collected more than $2 million with the cameras, the city's police department has jumped aboard. Two cameras it recently purchased will be used to find stolen vehicles.

O'Leary, who since 1984 has been Arlington's elected treasurer, said the device has already helped his office collect $180,000.

"These are not nice people," said O'Leary. "They have no intention of paying."

Unlike the cameras that until July 1 were used by several Northern Virginia communities to catch red-light runners, the one being used by Arlington and Alexandria has not alarmed some civil libertarians.

The red-light cameras snapped photographs of vehicles whose drivers were breaking the law, and the drivers were guilty until proven innocent, they argued. Instead, the BootFinder camera, as it is called, simply expedites the jobs of parking enforcement officers and tax collectors.

"The way this technology is being used now is not problematic, but how the information is used could make it a concern," said Kent Willis, executive director of the American Civil Liberties Union of Virginia. "It's like trying to argue against a typewriter. If it's going to make a job easier, it's tough to argue against."

Marc Rotenberg, executive director of the Washington-based Electronic Privacy Information Center, agreed but added that long-term issues could arise if the users delve into other databases, like one that might help authorities find people who owe child support. "I'm concerned about where this can lead," he said. "I don't think the privacy issue with the license plates is as great, but there need to be limits to the access" of detailed and private data.

This week, as his partner drove, Cortez aimed the camera at lines of parked cars and checked the tag numbers against the database, which the treasurer's office uploads weekly. The list contains the names of people with delinquent vehicle property-tax bills and unpaid parking tickets, and if a match is made, the robotic voice of a woman announces the find.

"Lock! Lock! Lock!" the voice screams as the offending license plate is highlighted and then frozen on the screen.

If a lock is made on a vehicle that is moving, the tax collectors and parking enforcement officers do nothing to stop it because they don't have the authority to flag it down. But if they come across a vehicle that is parked, the jurisdictions employ different tactics to ensure that the debts are paid.

In Alexandria, because the camera is being used only for parking enforcement, the vehicle is booted at the scene. Cortez and the other tax collectors in Arlington remove the license plates and affix a bright green sticker to the windshield, blocking the driver's view.

It informs the owner of the unpaid fines, whether for personal property taxes or unpaid parking tickets. After three days, if the fines are not satisfied, the vehicle is towed and a date is set for it to be auctioned, Cortez said. Tax collectors in Virginia have the authority to seize the vehicle, and any other personal property, to satisfy outstanding debts, he said.

The device was created under a Justice Department grant by Andrew Bucholz, a former Alexandria police officer. His Alexandria-based company, G2 Tactics, has sold the devices to four governments nationwide, including two cities in Connecticut.

Bucholz came up with the idea after leaving the department in 1993. Frustrated with the tedious process of locating stolen vehicles -- back then an officer had to call a dispatcher and read the tag number of a suspicious vehicle aloud -- Bucholz imagined a gadget that would do the work for them. It would indiscriminately scan the license plates of every vehicle, paying zero attention to its make, model or driver.

But the camera didn't sell.

"It was like trying to sell magic beans," Bucholz said. "I would give my spiel, tell everyone everything it could do, and they would say, 'No, I don't believe you.' "

After a demonstration for authorities in Arlington, it was not the police who expressed interest, but O'Leary -- an unexpected client.

Before he learned of the camera, O'Leary said, his office went about collection efforts in more conventional ways, through mailed notices and repeated telephone calls -- efforts he can now supplement with the BootFinder system.

In an era in which technoscientific tools are introduced almost monthly to police departments across the country, other government agencies have mostly gone about their business in far less fancy ways.

But this thing, O'Leary said, he had to have.

"No doubt about it, it was going to make our jobs easier," he said.

O'Leary said the county hopes to soon add to the database a list all of those people who haven't returned library books on time.

"It's not the fines, necessarily, that we're after," he said. "It's the books.

"The county owns them, and we're talking in some cases $400 to $500 worth of books that a person is able to check out at one time. If you don't return them and you ignore the notices from the library, in frustration, the libraries turn the debts over to us. It's surprising how quickly [books] show up in our night deposit box when we start warning them about what could happen."

Andrew Bucholz's BootFinder camera allows parking enforcement officers and tax collectors to locate people who have unpaid fines.Moses Cortez uses the BootFinder camera to track down people who have failed to settle their debts to Arlington County.