City business leaders teamed up with a San Francisco tech company called Arrivalist to keep tabs on people's cellphones.
They're trying to create data on consumer behavior to inform strategies to bring in more visitors.
They are able to tell what cities tourists come from, and how many nights they stay.
"The data is aggregated and anonymous. So we don't really track individuals, as much as aggregated data," said Bob Lincheid with Walnut Creek Chamber of Commerce. "It's information by location only, and no demographic personal information is even gathered or shared."
A few other local cities are already using the same platform, including Sonoma and Stockton.