Twenty years ago, Herb Sorensen had his great flash of insight into how people shop. The researcher of customer behavior sat in his living room leafing through an old Time-Life book, when a picture of cars moving through an intersection caught his attention. The headlight beams crisscrossed in the dark.

Those cars could be shoppers, pushing carts around a store, he thought. The beams, captured by time-lapse photography as an intricate web of white lines, could show the paths the shoppers take as they maneuver their carts through aisles, searching for cereal or mustard or a quick-cooking casserole mix to fix for dinner.

"I could see all the lines moving, and I wanted to see, where do people really go, and what do they really do," he remembers. That has led to work that "has been rewarding intellectually beyond my imagination."

Yet only in the last year has Sorensen, who holds doctorates in biochemistry and biophysics, seen the technology emerge to make this dream come true. It's a wireless system called PathTracker that Sorensen's company developed in conjunction with the WhereNet Corp. of Santa Clara, Calif., which helps companies manage "mobile resources."

Systems such as that used by luxury goods retailer Prada use radio waves and antennas in tags to determine when an object has passed a given point. WhereNet's technology takes the radio approach a step further, following an object around, anywhere within a 250-foot radius of an antenna. Its Real Time Location System can show where the object is at any given moment, within 10 feet, depending on the environment.

Using PathTracker, Sorensen realized most people in the Thriftway Store in Troutdale, Ore., where he lives, prefer to shop the aisles starting from the back, not front. That pattern had escaped him in all the years he tracked shoppers with pencil and paper. Now, Thriftway displays that advertise daily or weekly specials point toward the back of the aisles.

"I'd tried to track these movements manually, but it was too hard," Sorensen says. "We're uncovering secrets hidden in plain sight."

Merchants are hungry for the data that researchers like Sorensen can provide, even without a guaranteed return on investment. Kroger, which acquired two big chains in the Pacific Northwest where Thriftway competes, for instance, manages to clear just 2.2 cents of net profit on each dollar of sales. Independents, like Thriftway, have to scratch for every possible advantage in such a climate.