Chances are you have a supermarket shoppers' club card in your wallet, or on your key chain.
When they use them, shoppers get rewards, or discounts, and supermarkets can track buying patterns.
In New York, those cards saved thousands of people more than cash - they saved their health!
When managers at a Wegman's market in Williamsville,New York, near Buffalo, found out that a worker in the produce section had hepatitis A, they checked their shoppers club data for anyone who bought produce.
Within a few hours, they had a list of nearly 15-thousand customers, and began making contact with them, explaining the situation.
Although chances of passing on the Hepatitis were very slim, many of those customers came to a local medical center to get vaccinated.
Wegman's officials say this was a "natural" use for the card.
