Hill Country Galleria in Bee Cave, Texas, used the information to determine that a lot of shoppers owned pets. So it installed water fountains, babysitting stations and "Santa Paws'' photo ops for furry friends. The time customers spent in the mall rose by 40 percent, according to CBRE Group Inc.

A shopping center in Chicago found it was drawing customers from Asian neighborhoods, so it decided to fill a vacancy with a high-end Asian specialty grocer..

Dunkin' Brands Group Inc., which opened 278 new doughnut shops in the U.S. last year, employed phone data to make sure the new stores wouldn't siphon customers from existing locations.

Retailers are following the trail of electronic bread crumbs left by millions of customers. And it's helping them at a time when the industry is suffering.