Battery-powered, ultrasonic transmitters. Small enough for a key chain or a belt, they're worn by people or placed inside objects. They broadcast a 48-bit pulse to receivers that are embedded in ceilings.
Here's how they work: By using the speed of sound, the receivers compare the transmitter's arrival time at three or more locations and calculate the wearer's precise position. A computer then uses this location information to create zones of "usage" and "availability" around objects and people. For example, if a person's zone overlaps an object's zone, the person becomes the temporary "owner" of that device (whether it is a workstation or digital camera). So, there is no need to log on, and whatever you create using that device (such as a document or a picture) is automatically stored on a server in your personal file. Far out. About 800 bats are in use at the AT&T Lab in Cambridge, England.