Background: The ASSURE® wearable cardioverter defibrillator (WCD) is designed to protect patients at risk of sudden cardiac death while minimizing false positive shock alarms (FPAs), which can undermine confidence and reduce adherence. Although the original ASSURE Detection Algorithm (ADA) demonstrated robust performance, post-market experience identified opportunities to further reduce FPAs without compromising ventricular tachycardia/fibrillation (VT/VF) sensitivity.Objective: To develop and validate a revised ADA that reduces FPAs while preserving VT/VF sensitivity, using stored ECG episode data obtained from ASSURE WCD patients.Methods: Algorithm refinements focused on improved supraventricular tachycardia discrimination, enhanced noise management, and more accurate QRS identification. Development incorporated a high-fidelity virtual model for rapid iteration, and validation was performed using a physical WCD device model. Comparative validation relied on the measurement reliability of the WCD models to enable controlled evaluation of arrhythmia classification performance. Sensitivity, and per-episode and per-patient FPA rates as measures of specificity, were assessed using a real-world ECG dataset and corroborated with datasets used for original algorithm testing.Results: The revised algorithm detected 100% of shockable VT/VF rhythms (137 episodes) in the Field Episode test dataset. In > 8,000 non-VT/VF Field Episodes, the revised ADA reduced per-patient total FPAs by 51.9% (95% CI 43.8–60.0) and sustained FPAs by 69.4% (59.2–78.3). Testing with legacy datasets confirmed continued compliance with standard performance criteria.Conclusion Using a controlled comparative validation methodology, the revised ADA demonstrated substantial reductions in FPAs while maintaining high VT/VF sensitivity, supporting improved patient experience, adherence, and reduced exposure to potential inappropriate therapy.