If that sounds a little like Big Brother is watching, he might be.

"Cameras are the equivalent of hundreds of sets of eyes," Mayor Richard Daley said Thursday. "They are the next best thing to having police officers stationed at every potential trouble spot."

The system would exceed existing projects in how it would tie cameras to emergency operations, said Ron Huberman, executive director of the city's Office of Emergency Management.

Neither the courts nor the American Civil Liberties Union (news - web sites) have objected to cameras in public places, saying there is no expectation of privacy on a city street.

"We live in a video world," said Ed Yohnka of the ACLU of Illinois.

The high-definition, motorized cameras can rotate 360 degrees and include night-vision capability. They will be mounted on buildings and utility poles across the city.

Most are already in use - 30 by the police department and 1,000 at O'Hare International Airport. Other cameras are on elevated train platforms and the city's 600 schools. An additional 250 cameras yet to be installed will raise the number to more than 2,000.

The city is also considering allowing private companies to join the network, for a fee. Officials said the system size is nearly limitless.

The linchpin in the network - paid for with a $5 million grant from the U.S. Department of Homeland Security and scheduled to be up by March 2006 - is software designed to detect "suspicious" activity.

For instance, if someone left a suitcase in a stairwell, the software would engage any camera within range and alert a worker at the emergency operations center. It would do the same if an individual rushed up to another and dragged him away. A series of cameras could track fleeing criminals, and 911 operators would be able to give police descriptions of suspects.

Huberman said the cameras will also allow city departments to be more vigilant. Public works will be able to spot a broken water main instantly or the transportation department can see traffic jams developing.

"It really adds a whole new tool to public safety," Huberman said. "It gives us a tremendous early warning and detection capacity."

Chicago is the first U.S. city to install such a network.

Officials here said they studied systems used by Las Vegas hotels and casinos, as well as the Pentagon (news - web sites) and the city of London, where it's said that the average resident is viewed by 300 cameras a day.

Baltimore is trying to build a network with around-the-clock surveillance cameras. Other cities have used them during big events.

Police in Tampa tried the cameras, using a mug shot database and facial recognition software to identify criminals on the street. It abandoned the effort after two years because it never identified a wanted criminal.

Huberman said Chicago considered face-recognition technology but rejected it as inefficient and immature. But, he said, it's a possibility in the future.

"Chicago has a history of pioneering 911 operations," Huberman said. "Now, we're stepping off in the direction where 911 operation is going to be in the future."