Cybersecurity expert explains how signal sniffer is being used in search for Nancy Guthrie

As the search for "Today Show" host Savannah Guthrie's mother, Nancy, enters its third week, new evidence in the form of a glove was found near her home.

The family has been ruled out as suspects in her disappearance, and now the feds have deployed a so-called signal sniffer aimed at locating her pacemaker.

But how does something like that work? A cybersecurity expert said even if pinging her pacemaker is a long shot, at this point in the investigation, every available tool is going to be used.  

Law enforcement sources confirm investigators are using what's known as a signal sniffer attached to low-flying helicopters in an effort to detect transmissions from Nancy's pacemaker.

"It's going to be a quite weak signal. Typically, that signal goes a few feet," said Jim Jones, cyber security and digital forensics expert. "You're kind of pulling out all the stops and saying, well, this might work, and it might."

Jones, who is also an associate professor at George Mason University, said that, along with a weak signal, pacemakers transmit at irregular intervals.  

"And the last thing that makes this a long shot, but not implausible, is that the signal's not going to carry an overt identifier. It's not going to say, you know, I'm Nancy's pacemaker. So they're going to possibly detect a lot of signals," he said.

The FBI is analyzing male DNA found on the black glove found near Nancy's home. Investigators are now trying to match it to the male DNA inside the house to prove it belonged to the suspect.

"If they're able to match the DNA from inside that residence with the glove they found on the outside. Then that's where you got the home run," said Jason Pack, retired FBI special agent.

The Pima County sheriff said Nancy's family has been cleared as suspects. This comes after Savannah made an emotional plea over the weekend.

The sheriff confirmed his investigators are reviewing surveillance from Walmart stores and are examining purchase records of every Ozark Trail hiker backpack purchased online and in stores. The suspect's facemask may have also come from the same retailer.

"If that's the case, that's going to really narrow it down, and hopefully that's what they're working with, the corporate security folks at Walmart to find out," Pack said.

The sheriff says the Guthrie family and their spouses have been cooperative throughout the investigation and are victims in this case. 

Investigators are sifting through more than 50,000 tips that have come in since Nancy went missing.