Global positioning satellite systems don’t work well in skyscraper-filled urban canyons and not at all inside buildings. Rosum, a California start-up firm, aims to fill that gap using television signals, according to an article in the San Jose Mercury News. TV signals penetrate through buildings, and Rosum uses them to track people where GPS can't. The first device using Rosum's technology is in the prototype stage. Navigation products using it will make their debut next year, according to Rosum Chief Executive Skip Speaks.Rosum, which counts among its investors In-Q-Tel, the investment arm of the Central Intelligence Agency, promises a vast improvement in location-tracking services and gadgets, according to the report. That could help everyone from the military to dispatchers tracking delivery trucks. It could be used to track people indoors or locate someone making a 911 emergency call on an Internet phone.Adds Speaks, the former head of Kyocera's wireless phone business, “Ultimately, we'd like to drive the technology into every cell phone,” says Speaks.