User Authentication Using Inner Wrist Skin Prints: Feasibility and Performance Assessment with Off-the-Shelf Fingerprint Sensor

Wrist-worn devices enable new paradigms of implicit and continuous user authentication; however, identifying biometric modalities that combine security, robustness, and practical integrability remains challenging. Inner wrist skin texture represents a largely unexplored biometric trait with potential for unobtrusive authentication using commodity hardware. This study evaluates biometric authentication based on inner wrist skin texture using an off-the-shelf capacitive fingerprint sensor and a closed, manufacturer-provided verification algorithm. Two experiments were conducted. Experiment 1 assessed baseline authentication performance under controlled acquisition conditions in a cohort of 33 participants (21 male, 12 female; mean age 30.0 ± 16.9 years, range 10–71 years), yielding 1,768 authentication trials. Experiment 2 evaluated robustness to wrist posture variation under controlled wrist flexion in a separate cohort of 15 participants (11 male, 4 female; mean age 30.9 years, range 18–49 years), with 3,900 authentication trials recorded. Across 86,897 impostor comparisons in Experiment 1, no false acceptances were observed, corresponding to an upper false acceptance rate below 6.7 × 10⁻⁵ at a 99.7% confidence level, while the false rejection rate was approximately 2.93%. In Experiment 2, the overall false rejection rate was 3.52%, with no systematic dependence on wrist angle. These results indicate that inner wrist skin texture is a highly discriminative and geometrically stable biometric trait suitable for practical wrist-worn authentication systems.