On a Tuesday morning in July 2015, a swarm of FBI investigators and state officials combed through a large white-brick house in suburban Indiana.

After they finished their initial sweep, a new detective was brought in. He was an altogether different species of investigator: A black Labrador retriever named Bear, who set about sniffing in corners of the house. The dog had previously spent some 8 months training to smell electronics, specifically USB thumb drives, memory sticks, SD cards or other small storage systems that could hide digital contraband.

Humans had been removing electronics from the house all morning, though later inspection of these items would be less fruitful than hoped. But, with a handler in tow, Bear froze in front of a secret hiding spot. There, tucked away, officials found a thumb drive. The contents the device held would later be used to convict ex-Subway spokesman Jared Fogle, who was sentenced to 15 years, eight months in prison for possessing child pornography and sexual conduct involving minors.

"You think about investigators going into a house and trying to find a microSD card that is as big as a fingernail," Bear's trainer Todd Jordan told Fox 59 in July. "It will take investigators hours, especially if someone is trying to hide it."

At the time, Bear was one a handful of dogs in the country able to follow its nose to external computer storage. Sometimes dubbed "porn dogs," due to the cases in which they are frequently deployed, the animals do not actually sniff out illegal pornography but a faint chemical in storage drives. Because the odor is tough to detect, the training time is longer than that for narcotics - about a half to three-quarters of a year, according to Bear's trainers at Tactical Detection K-9.

The dogs do not come cheap. The Seattle Police Department purchased Bear for $9,500 in the wake of his famous bust.

During the time since, the ranks of electronics detection dogs has swelled, almost doubling over the past year - to nine certified electronic detection K9 units across the U.S. The latest to join these elite canine ranks is URL (it's pronounced like "Earl"), a black Lab who was rescued from a shelter as a puppy. Taught by the same group as Bear, URL will assist the Weber County Sheriff's Office in Utah.

"Specially trained to sniff out electronic storage devices such as thumb drives, cellphones, SIM cards, SD cards, external hard drives, tablets and iPads, URL offers a unique set of skills to aid investigators in fighting crime," the sheriff's office wrote on Facebook. "Whether it's child porn, terrorism intelligence, narcotics or financial crimes information, URL has the ability to find evidence hidden on basically any electronic memory device."

It is a trade secret exactly which chemical URL and Bear are sensing, though it is possibly an adhesive commonly used to manufacture USB drives and microSD cards. The FBI contacted Tactical Detection K-9, trainer Dennis Clark told Fox News' Gretchen Carlson in August, to see if dogs could smell storage drives. An unnamed laboratory isolated a compound from the memory devices, and the trainers imprinted the chemical scent on Bear and other dogs.

The dogs are a new phenomenon in the world of canine detection. Australia -- a pioneer in breeding detector dogs -- has yet to teach a pooch to smell computer drives, Steve Austin, who has spent 30 years training detection dogs for police, environmental agencies and others, told The Washington Post.

Although it may seem intuitive that pungent drugs like marijuana could be sniffed out, humans don't normally associate our iPhones with a particular smell. But dogs that sense electronics are not completely unheard of. The Motion Picture Association of America paid trainers to teach a pair of black Labrador retrievers, named Flo and Lucky, to sniff the polycarbonate in DVDs. As of 2008, the dogs had participated in 35 raids totalling 1.9 million pirated DVDs (the pooches cannot, however, tell a bootleg disc from the real thing).

Austin, for instance, has trained dogs to detect SIM cards and mobile phones in prisons, where the devices are forbidden. He uses a technique he calls scent generalization. "You get numerous mobile phones with numerous scents all over them," he told The Post, "and train the dog to find as many phones as we possibly can." The dog does not learn "generalized Apple or old shoe or heroin - it's generalized mobile phone."

Dogs are about 10,000 to 100,000 times more sensitive to odor than humans. Where we might smell a soup, a dog could pick out the scent of chicken and the noodle wheat and the individual seasonings. From their comparatively larger nasal cavities down to a microscopic level, dogs are built to smell. One canine trainer told the Australian Broadcasting Company that if you took all the olfactory receptor cells out of a human and spread them with a butter knife, you would get a schmear the size of a first-class stamp. A dog's smelling cells would cover a tea towel.

In some respects, it is unsurprising that dogs would be able to smell electronics -- after all, they can detect low blood sugar in people with diabetes, orca whale poop a nautical mile away and bed bug infestations. Looked at under a different light, however, we have just scratched the surface. It is only in recent years, Austin says, that trainers have begun to explore the limits of what dogs can detect. He was recently stunned to see his dogs track rare eastern bristlebird nests in the Australian wilds, as he had trained the pups on a handful of old feathers and musty droppings from captive birds.

"We're starting to push the dog into situations we never thought possible before," Austin said. "I think we limit our dogs to our own capabilities. And I'm no Einstein or Hawking." He would "love to see what a genius like Stephen Hawking could do" with a detection dog.