Biometrics in Wearable Devices: Heart Rate and ECG as Identifiers

Wearable devices are increasingly exploring cardiac signals, particularly heart rate patterns and electrocardiogram (ECG) waveforms, as a biometric identifier. Unlike a fingerprint or face, a cardiac signal can be captured continuously and unobtrusively from a wrist-worn or chest-worn sensor, opening the door to a passive, always-on form of identity confirmation.

The heart's electrical activity and the resulting rhythm of contractions are shaped by the individual's specific cardiac anatomy, including the size and orientation of the heart, and the exact pathways electrical signals travel through it. This produces a waveform pattern that varies meaningfully between individuals, similar in principle to how fingerprint ridges vary, even though the underlying biological mechanism is completely different.

• Photoplethysmography (PPG): an optical sensor, common in fitness trackers and smartwatches, that measures blood volume changes in the wrist to infer heart rate patterns
• Single-lead ECG: a more precise electrical measurement requiring the user to touch two electrodes simultaneously, found in higher-end smartwatches
• Chest-strap ECG monitors: used in medical-grade and athletic contexts, offering the cleanest signal for biometric purposes

A major appeal of cardiac biometrics is that they support continuous authentication rather than a single point-in-time check. Because a wearable can sample the wearer's cardiac signal repeatedly throughout the day, it can maintain ongoing confidence that the device is still on the original wearer's body, automatically locking sensitive functions like payment approval if the device is removed or the signal no longer matches the enrolled pattern.

Cardiac signals change with physical exertion, stress, illness, medication, and age in ways that fingerprint or iris patterns generally do not, requiring matching algorithms to be considerably more tolerant of natural variation, which in turn can increase false acceptance risk if not carefully tuned. Signal quality from wrist-based optical sensors is also lower than dedicated medical ECG equipment, and motion artifacts from daily activity can degrade capture reliability, meaning cardiac biometrics today are generally positioned as a supplementary factor rather than a sole authentication method.

Cardiac biometrics are most actively explored in wellness and fitness ecosystems, where a device already collects heart data for health tracking, making biometric identification a natural secondary use of data already being captured. Research also continues into combining cardiac signals with other passive wearable signals, such as gait detected through an accelerometer, to build a more robust multimodal continuous authentication profile without requiring the user to take any explicit action.