America's largest retailer is adding another technological level to its stores. Following on from its biometric payment system and possible RFID shelving, Wal-Mart is to introduce infrared technology in its stores as a way of measuring the effectiveness of its various promotions.

Known as Prism, the system was crafted by large suppliers including Coca-Cola, Kellogg's, Kroger, Procter & Gamble, Walgreens and Disney in order to "track shoppers' movements around the store" and compare them to actual sales in order to define how effective the promotion was.

In other words, if customers linger for a while in front of a certain display before ultimately buying a product, they want to know it, and use that info in the future.

The various firms have persuaded Wal-Mart to install a trial system in 10 of its SuperCenters, with a much broader rollout expected to follow soon.

Wal-Mart (obviously) hopes that the system will enable it to attract more advertising money to its in-store promotions.

So remember that Big Brother could really be watching as you rush to the two-for-one promotion on Special K cereal. Anna Lagerkvist