Why retailers wanted to follow the cart
A shopping cart traces a shopper’s route more directly than a checkout receipt does. A receipt records what someone bought, but not which aisles they passed through, where they stopped, or how long they browsed before choosing an item. By attaching GPS trackers to carts, retailers hoped to map those movements and use them to decide where products and aisles should go.
The idea depended on getting a reliable location for each cart as it moved. If the position readings were accurate, a store could compare traffic across sections and see whether shoppers lingered in one area or moved quickly through another.
Why the signal fell apart indoors
GPS works by calculating a receiver’s position from radio signals sent by satellites. Those signals are weak by the time they reach Earth, and they work best with a relatively clear path from the sky. A large supermarket blocks that path with a roof and walls. Signals that do get inside may bounce off surfaces, making it harder for the tracker to tell where the cart actually is.
That creates a basic problem: a location trace that jumps around or places a cart in the wrong part of the building cannot reliably show which aisle attracted attention. The tracker might record movement, but not the useful, aisle-by-aisle pattern retailers were trying to measure.
The experiments therefore ran into a mismatch between an outdoor positioning tool and an indoor question. To rearrange a store based on shoppers’ routes, retailers need dependable location data inside the building—not simply a trail of coordinates that becomes unreliable once the cart passes through the doors.
