They're small, smart and vigilant, the sort of miniature technology that science fiction writers once dreamed of. But the battery-powered, wireless sensors sometimes known as "smart dust" are here, and they're making their way into the electronic fabric of our lives.

In the last few years, smart dust sensors smaller than a deck of cards have been deployed in research projects to monitor the vibration of manufacturing equipment, keep tabs on colonies of seabirds and measure fine variations in vineyard climates that can make or break a wine.

Now they're being sold for real. Dust Networks Inc., a chief developer, said this week that defense contractor Science Applications International Corp. of San Diego would become one of its first customers, using the technology for perimeter security systems. A grocery chain in Minnesota installed the sensors in August to monitor energy use. A competitor, Sensicast Systems Inc., just announced its own arrangement to provide sensors to monitor the environment at a nuclear generating station.

Those deals resonate in an industry that didn't exist until a few years ago. Industry analysts predict that micro-sensors -- which communicate via radio-linked networks like computers on the Internet -- will become as ubiquitous in their own way as personal computers on the World Wide Web.

To be sure, sensors have been around for decades, particularly in the manufacturing world. But they've been costly, relatively large and limited by the wires that connected them to centralized monitors. As a consequence, they were generally used by companies with deep pockets.

In recent years, as the cost of computing plummeted along with the size of computing machines, science fiction fantasy quietly morphed into technological fact. Starting in academic labs at the University of California at Berkeley and elsewhere, development of smart dust (a whimsical name that suggests where inventors hope the technology is headed) has spread to the government and private sectors.

The capabilities vary. Some take pictures. Others serve as sensitive thermometers. There are even tiny sensors that can detect the presence of gunmetal and tanks. Some analysts and researchers believe that networks of these diminutive monitors may eventually link refrigerators, printers, car keys and other everyday objects to the Internet, enabling observers and other machines to keep track of them remotely.

"It's vast, in terms of the possibilities," said Glen Allmendinger, president of Harbor Research Inc., who predicted that sales of smart dust and related technology would grow from about $10 million this year to billions by the end of the decade.

"Homeland security is going to be a big part of it, but there are so many other applications," said Craig Mathias, an analyst at the Farpoint Group, an advisory firm specializing in wireless communications and mobile computing. "Is it going to be a $1 billion business? Absolutely."

It's not just technology enthusiasts and executives at tiny companies who are excited. The Defense Advanced Research Projects Agency has spent millions on university studies. Earlier this year, the CIA's venture capital arm, In-Q-Tel, bought a stake in Dust Networks. Technology researchers at the Department of Homeland Security have made sensors a priority. Even computer chip giant Intel Corp. is working on wireless networks of sensors.

"Wireless sensors have moved out of the labs," said Intel spokesman Kevin Teixeira. "The technology is being figured out."

Researchers said the devices, also known as "motes," can include any number of sensors to track activity or assess the surrounding circumstances, such as weather, light and heat. When the devices collect meaningful information, their systems turn on a low-power transmitter and broadcast the data to the next closest device, up to about 100 feet away. Researchers and analysts claim the devices can sometimes operate for up to three years on a pair of double-A batteries.

If one device in the network fails, the data are picked up by another one, an echo of the sort of redundancy that makes the Internet so reliable. Dust Networks officials call it "smartmesh." They say their software is designed to enable a central PC or laptop to fuse or triangulate reports of the same activity from different angles within the network. In doing so, they said, the network can determine with far more nuance the direction a person is moving, the weight of a vehicle or even the likelihood that a machine is failing.

"This is no longer futuristic. This is real deployment for real customers," said Kris Pister, an electrical engineering and computer science professor at Berkeley who began studying smart dust in 1997. He founded Dust Networks two years ago. "It's a huge threshold to have a product we can actually shop to customers."

Researchers still face formidable technological challenges. Communication can be disrupted by hills or electrical interference. Developers have to figure out how to ensure the increasingly tiny machines don't burn through their meager power supplies too quickly, or overwhelm the networks with false alarms. In addition, the devices can still cost hundreds of dollars, scaring away some potential customers.

But analysts said they're making progress. In 2002, researchers from the Intel Research Laboratory at Berkeley linked 32 sensors about the size of a prescription bottle to the Internet to take readings of the weather on Great Duck Island, Maine, and to assess the condition of nesting burrows used by local seabirds known as Leach's storm petrels. In the second season last year, they used more than 150 second-generation sensors that were smaller than size-D batteries.

"These networks monitor the microclimates in and around nesting burrows used by the Leach's Storm Petrel," said a report on the project. "Our goal is to develop a habitat monitoring kit that enables researchers worldwide to engage in the non-intrusive and non-disruptive monitoring of sensitive wildlife and habitats."

In August, two dozen Dust sensors were installed in a Supervalu grocery store in suburban Minneapolis. That network is monitoring temperatures and energy use, which typically accounts for the second-largest cost of operating a grocery store.

As for SAIC, it's adopting "smartmesh" sensor networks to create electronic perimeter systems for defense and intelligence customers. Thomas J. Sereno Jr., manager for the SAIC monitoring systems division, said tests found the technology can use small magnetometers to detect whether someone is carrying a gun. SAIC plans to use microphones to search for "acoustic signatures" of vehicles, moving groups of people and such. Sereno said it also will build in cameras of the sort used in mobile phones.

Sereno speculated that some SAIC clients may use unmanned airborne vehicles to fly over rugged and dangerous environments and deposit the technology. SAIC will also be pitching it for homeland and border security. He said the ability of the network to be "self-healing" if some of the devices fail is appealing. The company intends to unveil a model for customers next month.

"If you combine all the information from these sensors and fuse it, you can make inferences," he said. "We're starting to get the firm belief this is truly going to work."

Intel's 1.1-inch-square mote prototype includes an antenna (1), a Bluetooth radio (2) and sensors (3). At left, the mote connected to its battery unit.