Imagine walking down the street and browsing the contents of a store by pointing a handheld computer at it. Up pops a list of available products and services, and even comments from customers. At Hewlett-Packard Laboratories in Palo Alto, CA, engineer Salil Pradhan’s team has developed such a mobile interface. The software runs on a personal digital assistant or cell phone, automatically linking to Web sites associated with nearby buildings. Unlike tracking systems that use bar codes or radio frequency ID tags, Pradhan’s device works at distances greater than 10 meters; it calculates the user’s position and orientation using a Global Positioning System receiver and a digital compass embedded in the handheld. Pradhan is expanding the system to work indoors. A product could be available in three years, he says.