Personal location devices are beginning to catch on, largely because of a federal mandate that by late 2005, wireless carriers be able to automatically locate callers who dial 911.

Millions of cell phones already keep track of their owners’ whereabouts, using GPS signals. Analysts predict that as many as 42 million Americans will be using some form of “location-aware” technology in 2005.

“We are moving into a world where your location is going to be known at all times by some electronic device,” said Larry Smarr, director of the California Institute for Telecommunications and Information Technology. “It’s inevitable. So we should be talking about its consequences before it’s too late.”