Police departments in the US are using canines to sniff out thumb drives, phones, and other electronics. They train search dogs to associate food with locating the faint chemical smell of electronic devices, as detailed in this report by CNET.

It’s a lesser-known use for the K-9 programs across the country. It was kept secret for years so that authorities could catch unsuspecting criminals without running into complications and so they could be sure the dogs weren’t making mistakes. One case in 2015 did bring attention to dogs finding hardware through their olfactory senses. A Labrador retriever named Bear uncovered a man’s flash drive that contained child pornography, which helped make the case for the man’s conviction.

A K-9 instructor for the Connecticut State Police told CNET that out of every 50 dogs tested, only one usually has a strong enough nose to identify the weak scent in electronics; specifically, they’re looking for the chemical compound triphenylphosphine oxide, which can be found in all gadgets that contain memory. The instructor said that electronics are harder to sniff out than bombs, drugs, humans, or flammable liquids. In particular, Labrador retrievers tend to have the excellent snouts that are required for the job. Dogs that are able to detect the scent are known as electronic storage detection (ESD) dogs.

The Labrador retriever Harley, who CNET observed, gets fed a few pieces of kibble for each device she sniffs out. On days when there’s nothing to search for, her carriers will train her by hiding devices throughout the house. Once a week, she gets a treat day where she’s fed without having to earn it. But otherwise, they keep her on a tight regimen so that she’s motivated to search for thumb drives.

The dogs can find SIM cards that have a log of phone calls, find friends’ iPhones to replace the Apple feature, or even identify surveillance cameras in odd places like a coat hook. There are at least 17 of these ESD programs in the US that are used by local police and the FBI, and reports about the programs have increased in the last three years following the case with Bear.