A decade after failed attempts to computerize shopping, supermarket chains in the United States, Germany, and South Korea are rolling out new smart carts. The idea: Shoppers swipe their loyalty cards and a suggested shopping list pops up on the screen, based on their historical patterns.

If this works, markets could offer shoppers customized discounts. The challenge will be to convince shoppers that sharing this data is worth the benefits — and that this trove of information won't be sold to marketers elsewhere.