Instacart's Caper Carts bring fast checkout, coupons, and loyalty perks to Weis stores, but their cameras, location tracking, and in-aisle ads make the grocery cart feel like a data machine.

A Spectra Physics Model A supermarket scanner—one of the first ten ever produced. A laser within the unit projects a beam onto a mirror that redirects it through the glass plate on the top. Cade ...