Two new questions arise, courtesy of the latest advancement in cellphone technology: Do you want your friends, family, or colleagues to know where you are at any given time? And do you want to know where they are? Obvious benefits come to mind. Parents can take advantage of the Global Positioning System chips embedded in many cellphones to track the whereabouts of their phone-toting children. And for teenagers and 20-somethings, who are fond of sharing their comings and goings on the Internet, youth-oriented services like Loopt and Buddy Beacon are a natural next step. But ... if G.P.S. [makes] it harder to get lost, new cellphone services are now making it harder to hide. There are massive changes going on in society, particularly among young people who feel comfortable sharing information in a digital society," said Kevin Bankston, a staff lawyer at the Electronic Frontier Foundation. "We seem to be getting into a period where people are closely watching each other," he said. "There are privacy risks we haven't begun to grapple with." What if a boss asks an employee to use the service? Almost 55 percent of all mobile phones sold today in the United States have the technology that makes such friend- and family-tracking services possible. Consumers can turn off their service, making them invisible to people in their social-mapping network. Still, the G.P.S. service embedded in the phone means that your whereabouts are not a complete mystery. "There is a Big Brother component," said Charles S. Golvin, a wireless analyst. "The thinking goes that if my friends can find me, the telephone company knows my location all the time, too."