Photos: Interactive billboards

This promotion for Hilton Hotels lets passersby disrupt a virtual car race with their steps and hand motions. It's developed with technology from California company Reactrix Systems.

A crowd at San Francisco's Metreon theater stops to check out this interactive Jelly Belly billboard, created by Reactrix Systems. Each step sends virtual bellies swirling and floating in different directions.

A&E Television Networks ran this Reactrix promotion in New York's Grand Central Terminal one week over the summer. It promoted a new TV series called and gave the illusion of a liquid surface when people walked over it.