At some of the busiest airports, bomb-sniffing dogs are helping to speed up security lines.
Their knack for finding explosives is unparalleled.
The only problem is -- there aren't enough of them.
Eight-year-old black lab Sunny can easily detect the kind of homemade explosives used in the Paris and Brussels terror attacks.
She knows about 19,000 different kinds of explosives.
ATF Special Agent Sheila Fry is Sunny's handler.
"When I started in 2002 not too many people knew what a bomb dog was and now everybody has got a bomb dog," she said.
The use of bomb sniffing dogs by local, state, and federal law enforcement, as well as private institutions like universities, has steadily increased after the 9/11 attacks.
There are currently about 1,000 sniffing around U.S. transportation hubs. The K9s are specially selected, trained for nearly a year, and then serve for about eight years. But as demand around the world has increased, U.S. law enforcement has seen the market for available dogs tighten.
Doctor Cindy Otto runs the University of Pennsylvania's Working Dog Center.
"It really makes me concerned," said Dr. Otto. "I think we really have an obligation to the public to keep us safe, and the dogs we know are the most effective screening tool for explosives."
Recently Dr. Otto warned Congress of the potential for a looming shortage.
"One of the reasons for the shortage of quality dogs is we rely heavily on the procurement of dogs from other countries," she said. "To us, a national breeding program is a priority."
The Transportation Security Administration (TSA) used to have its own breeding program, but shut it down in 2012 due to high costs. Now the agency said it needs some 60 additional dogs to add to the more than 300 currently it's currently using.
Customs and Border protection said it needs an additional 325 K9 teams.
"We really need to think about a better way to provide these dogs," said Dr. Otto. "Because it really is a national security issue we are all invested in."
The TSA said they would like to add hundreds of detection dogs to our nation's airports in the coming years.