EXCLUSIVE: A former U.S. Marine and self-described “ethical hacker” has revealed he secretly built a custom Bluetooth “signal sniffer” device specifically to hunt for signals beaming from Nancy Guthrie’s pacemaker — and now he’s racing to turn the breakthrough gadget into a powerful mobile tracking app that could help locate countless vulnerable people in the future.

The whistleblower, who spoke to DailyMail.com on condition of anonymity to protect his ongoing work with law enforcement, says he sprang into action the moment news broke of the February 1 abduction from Guthrie’s Tucson, Arizona home.

“When this whole Nancy Guthrie case hit the headlines, authorities publicly confirmed her pacemaker had suddenly disconnected from her phone app at 2:28 a.m. — right around the time she vanished,” the ex-Marine explained in an exclusive interview. “That screamed Bluetooth Low Energy (BLE) tech, the kind modern pacemakers use to ping health data periodically. I knew right then: if we could sniff out that unique signal — every pacemaker has its own MAC address ‘fingerprint’ — we might pinpoint her location, even if she’s miles away or across a border.”

The device he cobbled together in his home workshop isn’t some off-the-shelf toy. It’s a portable, amplified Bluetooth receiver paired with a high-gain directional antenna and custom software that scans for faint BLE transmissions — the same low-power signals medical implants like pacemakers emit every few minutes to connect with nearby apps or monitors.

Law enforcement sources confirm “signal sniffer” technology — including airborne versions attached to low-flying aircraft — has already been deployed in the massive search effort involving the FBI, Pima County Sheriff’s Department, and hundreds of agents scouring the Arizona desert and beyond.

But this former Marine’s homemade version was built from scratch for one purpose: cracking the Guthrie case.

“I started with open-source Bluetooth scanning tools, beefed up the receiver sensitivity, added amplifiers to extend the range from a pathetic 10-15 feet to hundreds of yards or more under the right conditions,” he said. “Then I wrote scripts to filter for known pacemaker MAC patterns and log any hits with GPS coordinates. It’s crude, but it works — and authorities took notice fast.”

The invention comes at a critical moment in one of the most high-profile missing persons cases in recent memory. Nancy Guthrie, a spry 84-year-old who still drove herself to church and family gatherings, disappeared in the dead of night from her Catalina Foothills home. Security footage captured a shadowy figure tampering with her doorbell camera around the time of the abduction, and investigators believe she was taken against her will — possibly across the Mexican border, according to some FBI sources.

Her phone was left behind, but crucially, it had been receiving intermittent Bluetooth pings from her pacemaker until that chilling 2:28 a.m. cutoff. Experts say that’s when the device likely moved out of range — or was deliberately disconnected.

Enter the signal sniffer.

The technology exploits a little-known feature of modern cardiac implants: Bluetooth connectivity for remote monitoring. Manufacturers like Medtronic and Abbott equip many newer models with BLE to transmit heart rhythm data, battery status, and alerts directly to a patient’s smartphone app — no wires needed.

“It’s not a GPS tracker,” stressed one cardiologist familiar with the tech. “But because it broadcasts periodically, a sensitive enough receiver can triangulate the signal source if you sweep an area methodically.”

That’s exactly what the former Marine aimed to do.

He claims he reached out to investigators anonymously through secure channels, sharing schematics and test results from similar BLE devices. Within days, versions of his concept were being adapted for professional use — including drone-mounted and vehicle-based sniffers combing Tucson’s sprawling suburbs and remote desert outskirts.

Now, he’s taking it further.

“I’m turning this into a full-fledged app,” he revealed. “Imagine a smartphone tool that lets trained volunteers, search-and-rescue teams, or even family members scan for BLE signals from medical devices. With crowd-sourced data, geofencing alerts, and integration with public databases of device MAC ranges, it could revolutionize how we find Alzheimer’s patients who wander, elderly folks with implants who go missing, or kidnap victims wearing life-saving tech.”

The potential is staggering — and controversial.

Privacy advocates already warn that widespread BLE tracking could open doors to misuse, from stalking to unauthorized surveillance. But the Marine insists safeguards like opt-in registries, encryption, and law-enforcement-only access modes would keep it ethical.

“This isn’t about spying,” he said firmly. “It’s about saving lives. Nancy Guthrie’s case proves the tech exists — we just need to make it accessible and responsible.”

As the search enters its third grueling week, hope clings to every ping. Authorities have consulted pacemaker manufacturers for data logs, deployed genetic genealogy on DNA evidence found at the scene, and chased leads as far as Mexico. Online sleuths, psychics, and influencers have flooded tip lines, while Savannah Guthrie and family have pleaded publicly for her safe return.

Yet the former Marine’s secret weapon offers a glimmer of something new: technology born from desperation that could prevent future tragedies.

If his app launches as planned, it might one day bear a quiet tribute — perhaps even nicknamed “Nancy” in hushed developer circles.

For now, the hunt continues. Every faint Bluetooth blip could be the breakthrough that brings an 84-year-old grandmother home.

Nancy Guthrie, the 84-year-old mother of “Today” show co-anchor Savannah Guthrie, vanished from her Tucson home in what authorities call an abduction.

The Pima County Sheriff’s Department has made Nancy’s home a crime scene, with FBI agents and deputies combing the area for clues.

Modern pacemakers like the one Nancy Guthrie wears emit periodic Bluetooth signals for health monitoring — the key to the high-tech search effort.

Signal sniffer devices, amplified to detect faint BLE transmissions from medical implants, have been mounted on aircraft and vehicles in the desperate hunt.