The next time you walk into a shop, consider this:
You may not be using your phone, but it is giving out a unique signal that the retailer may be monitoring. A face scanner may check your age and gender while sensors pick up your body heat to help locate popular parts of the store.
Consumers have become used to players like Amazon closely following their shopping habits online, triggering targeted product recommendations, advertising and offers.
To counter the online threat, bricks and mortar retailers are playing catch-up, using increasingly sophisticated technology to improve staffing, layout and marketing.
Some people are less comfortable being watched in the offline world, prompting many in the business to promise to use only anonymised and aggregated data unless shoppers explicitly give their permission to be tracked.
But as retailers get more sophisticated and link the data they collect to loyalty card schemes, shoppers are starting to sign up to schemes that follow their movements in return for targeted discounts and apps that help them find products.