At top, an inactive (safe) food safety label. The horizontal line through the bottom bar code represents the scanner signal not reading the inactive bottom code. The bottom label shows the scanner signal not reading the top product label, while the bottom label has a wider bar at the left, indicating unsafe conditions.

Courtesy of Sira Technologies

Worried about those wieners? A “smart” bar code developed by two University of Rhode Island researchers and a food safety company will alert grocers and customers if packaged food has gone bad, the university announced yesterday.

The university said the bar code works through an ink that is nearly invisible, but turns red in the presence of food improperly refrigerated. The color change also keeps the bar code from being scanned at the checkout counter.

Brett Lucht, a URI chemistry professor, said there actually are two bar codes, the first of which operates when the pigment is activated. That will let the product be scanned routinely at the checkout. But if the food has risen above 40 degrees, the color change of the second bar code blocks the scanner.

Lucht and William Euler, a colleague in the chemistry department, teamed with SIRA Technologies, the food safety company, to modify an earlier discovery by the pair — a polymer that could be added to its products to make them change color when they were too hot to touch.

Lucht said the new product is not yet available commercially. He said SIRA is in the process of scaling up pigment production.

URI said its patent on the bar code could produce hundreds of thousands of dollars in revenue.

tmorgan@projo.com