Warning: This contains spoilers for episode two of The OA.

In “New Colossus,” the second episode of The OA, Prairie is approached by Dr. Hunter Hap while she’s playing violin in a New York City subway station. Hap makes the most of this chance encounter by asking whether her transcendent playing resulted from a near-death experience. Prairie is shook — what he said is true. Her curiosity leads her to follow him to a bar, where he drops some impressive knowledge about the uniqueness of heartbeats, which real-life scientists are applying to biometric security systems.

Hap, obsessed with near-death experiences and hearing the sound a body makes when it dies, pulls out a strange device that magnifies the sound of a heartbeat from 500 feet away while the pair are seated at Grand Central Station’s oyster bar. As Prairie slips on headphones and focuses the device on different people in the room, Hap quips, poetically: “You know, a heartbeat is more unique than even a fingerprint.”

Which is almost true. While heartbeats aren’t more unique than a fingerprint, scientists have known since 1964 that every person’s heartbeat is unique. Today, researchers are attempting to use that uniqueness to create new biometric identification systems. In other words, they’re turning pulses into passwords.

Hap lays out the device, along with some oysters.
Hap lays out the device, along with some oysters.

But first, a quick refresh on what makes a heart beat: The sound of a heart comes in two parts — there’s the “lub,” then the “dub.” The lub occurs when the heart’s mitral and tricuspid valves close; the dub happens when the pulmonary and aortic semilunar valves close. The difference in the characteristics of heartbeats stems from the vibrations of the walls of the heart and its major vessels, as well as the orientation of your valves. Whether or not your heart is beating faster because of exercise, if you looked a electronic scan of your heart, the waves would still look the same.

There’s some debate in the advantage in the uniqueness of heartbeats over other biomeasures. Andrew D’Souza, president of the biometric startup Bionym, told Wired that the most unique biometric is likely the retina of the eye, followed by fingerprints and an electrocardiogram measurement (ECG), which checks the electrical activity in the heart.

The sound of a heartbeat stems from the opening and closing of its four valves.
The sound of a heartbeat stems from the opening and closing of its four valves.

Even so, D’Souza and his company are placing their bets on the heart with Nymi, a wristband with an embedded ECG sensor that recognizes a user’s cardiac rhythm. The idea is that Nymi can be used to unlock devices — just like the fingerprint identification system on an iPhone. While it may be tricky to topple fingerprint security because of Apple’s monopoly, Bionym did released an Early Access Program in October for developers who want to start to use the tech before it’s commercial release.

The advantage that heartbeats have over other biometrics isn’t their uniqueness but the inability to replicate them. Unlike a fingerprint, someone’s ECG can’t be lifted from a smudge left on a glass. Likewise, you can trick a fingerprint scanner with a jelly replica, but you would have to trick someone into having their heartbeat measured by a ECG system to do the same.

In the future, passwords and pin numbers could be replaced by heartbeats. In the meantime, we’ll have to keep watching to see how Prairie’s own heartbeat is taken advantage of in The OA.

Photos via Netflix, Instagram/Giphy