A new piece of technology is now being used to detect spoilage and reduce food waste for supermarkets and consumers. The technology is a low-cost sensor that is linked to your smartphone, notifying it when your food goes bad.

Known as “paper-based electrical gas sensors” (PEGS), the sensors detect spoilage gases like ammonia and trimethylamine in meat and fish products. The sensors allow you to simply hold your phone up to the packaging to see whether the food is safe to eat.

PEGS were developed by researchers at the Imperial College London, who made the sensors by printing carbon electrodes onto readily available cellulose paper. When they were tested in laboratories, the sensors were able to pick up trace amounts of spoilage gases quickly and more accurately than existing sensors, at a fraction of their price. The researchers said that the sensors could one day replace the “use-by” date—a less reliable indicator of freshness and edibility. Lower costs for retailers may also eventually lower the cost of food for consumers.

“Although they’re designed to keep us safe, use-by dates can lead to edible food being thrown away. In fact, use-by dates are not completely reliable in terms of safety as people often get sick from foodborne diseases due to poor storage, even when an item is within its use-by,” said lead author Dr Firat Güder, of Imperial’s Department of Bioengineering.

“Citizens want to be confident that their food is safe to eat, and to avoid throwing food away unnecessarily because they aren’t able to judge its safety,” he continued. “These sensors are cheap enough that we hope supermarkets could use them within three years. Our vision is to use PEGS in food packaging to reduce unnecessary food waste and the resulting plastic pollution.”

“Use-by dates estimate when a perishable product might no longer be edible—but they don’t always reflect its actual freshness,” added Giandrin Barandun, also from Imperial’s Department of Bioengineering. “Although the food industry—and consumers—are understandably cautious about shelf life, it’s time to embrace technology that could more accurately detect food edibility and reduce food waste and plastic pollution.”

The researchers hope that PEGS will later have applications beyond food processing, like sensing chemicals in agriculture, air quality, and detecting disease markers in breath like those involved in kidney disease.