Thieves beware: The loot you stole just might be tracking you.

That's what happened in Lewisville recently, when two large air-conditioning units were taken from a new Centex Corp. housing development.

Unknown to the thieves, Centex security officials had hidden GPS – Global Positioning System – devices inside the units.

A homing beacon led police to a storage facility in Irving, where the stolen merchandise was found.

Bill Dunn, director of corporate security for Dallas-based Centex, said the GPS devices are a relatively new addition to the company's security plan and have already proved their worth.

"We've been successful right off the bat," Mr. Dunn said. "We've had at least two instances with successful results."

GPS devices, which rely on satellites to pinpoint locations around the globe, are better known for helping parents track teenage drivers and motorists navigate unfamiliar streets.

Now they're increasingly helping to catch crooks.

"It's being used more by law enforcement and private industry to track fleets and high-end merchandise," said Lewisville police Capt. Kevin Deaver, noting that the same technology is used in police "bait cars" to catch car thieves.

"In the beginning, GPS tracking devices were bulky and expensive," Capt. Deaver said. "Now they're more streamlined, concealable and easier to use."

There is also an economic factor.

Construction site theft costs the industry $5 billion a year, said Gopal Ahluwalia, vice president of research for the National Association of Home Builders, a Washington, D.C.-based trade organization.

To combat the problem, builders use guard dogs, install on-site cameras and delay installation of expensive appliances until construction is almost complete, Mr. Ahluwalia said.

GPS technology, he said, is one of the newest tools in their arsenal. "I would guess a lot of homebuilders are using it," he said.

Attempts to reach other area homebuilders last week were unsuccessful.

Mr. Dunn declined to say which brand of GPS unit Centex uses and was reluctant to describe how the stolen merchandise was tracked.

"It's basic GPS technology," he said.

The various GPS brands operate similarly, said George Karonis, president of LiveViewGPS Inc., a Valencia, Calif.-based company that sells a variety of GPS tracking and monitoring devices.

The wireless, self-contained units, about the size of a bar of soap, can be attached to any object and "are so small you wouldn't know it," he said.

When the units are tampered with or moved from an area, they alert owners through a text or recorded message sent to their phones.

At that point, "you would log on to a Web site to find out where any asset, person or vehicle is in real time," Mr. Karonis said.

Lewisville police were contacted about the missing air conditioners – valued at $2,000 apiece – at 11:30 p.m. on April 17.

Officers met with a Centex representative and were able to see the location of the stolen goods on a map on a computer screen.

"We located the storage unit in the early-morning hours of the 18th," Capt. Deaver said. Officers found three other air conditioners at the site and suspect they were also stolen.

The case is still under investigation, and no arrests have been made.