Earbud sensors can authenticate users by their heartbeat, study finds

AccLock is a continuous biometric-authentication prototype that uses accelerometer-captured ballistocardiogram (BCG) signals from earbuds to continuously verify the wearer; a 33-person study showed low single-digit error rates in many static and low-movement conditions and rapid detection when an earbud changed wearers. The system degrades with walking, running, talking, lower sampling rates (e.g., AirPods), and over longer-term drift; the paper did not test active spoofing, replay, long-term deployments, or address privacy implications and vendor access to raw sensor streams.