A shooting or stabbing occurs on Chattanooga’s streets, and gang members’ cell phones light up with text messages relaying the event.

“Witnesses text it before police even know about it,” said Sgt. Todd Royval, supervisor of the Chattanooga Police Department’s crime suppression unit.

Technology helps and hurts police officers as they attempt to track and apprehend gang members, he said. Many gang members use two-way cell phones and pay young children to alert them to police presence on a street. With enough warning, gang members disperse before police arrive, Sgt. Royval said.

Members communicate quickly about violence or drug deals, he said.

Drug dealers — in gangs or not — can text each other from opposite sides of town about a prospective buyer, including what car he drives and what he looks like, so the dealer can be prepared when the buyer arrives, said Antinio Petty, supervisor of the probation department for Hamilton County Juvenile Court.

Mr. Petty recently returned from a conference covering ways young people use technology — and it’s not limited to cell phones. The conference mostly focused on social networking sites such as Facebook.com and MySpace.com as they relate to young people.

Because young people can access the profiles of thousands of people across the country, they tend to emulate the flashy photos and criminal videos posted online, he said. Some show people shooting at other people; others show them using or selling illegal drugs.

Some pictures — especially those where young gang members pose with wads of cash or drugs — may cause nongang members to consider joining.

“These kids are very bright, and it’s truly a travesty that they’re using the good sense that they have for negativity,” Mr. Petty said.

But police also use technology to their advantage. Some officers have software in their in-car computers that allows them to pull up pictures of known gang members to match them with men and women standing in front of them, he said.

And with the advent of social networking sites on the Internet, police can keep tabs on gang members, including what affiliation they pledge and who their friends are.

Young people post pictures online at the risk of getting caught because they want to appear “cool” among their friends and fellow gang members, Mr. Petty said.

Many parents would be amazed to see the things their children post online, Sgt. Royval said. Many young teenagers have sites littered with gang symbols and colors and pictures of themselves throwing up gang signs.

“It’s helped out a lot for people who are adamant about saying they’re not a gang member and I pull up their MySpace account and they’re wearing gang attire and throwing up gang signs,” Sgt. Royval said.