Apple Watch Series 12 adds continuous heart sensing, readiness score, on-device AI

Apple’s Series 12 watch centers on a re-architected Health Sensing System paired with a new S11 chip, which Apple claims delivers the most accurate heart-rate sensing of any wearable, backed by a 1,000-person comparison study. The hardware samples heart rate every five seconds all day and measures heart-rate variability up to 24 times more often, splitting HRV into ‘recovery’ and ‘overall’ variants and feeding overnight and daytime vitals views. A new 0–10 readiness score—derived from activity, training load, vitals, and sleep, using data from the Apple Heart and Movement Study—translates that data into a daily recommendation.

Software is where the AI and privacy angles land. watchOS 27 brings Apple Intelligence-powered Siri to the wrist, and a redesigned iPhone Health app (US-only at launch) adds Insights and Longevity tabs, a ‘Health Age’ metric, and vision-based movement evaluations. Apple is also pushing into diagnostics, letting users book Quest lab panels covering 50-plus biomarkers for $119. New ‘Audio Intelligence’ features—meant to surface conversation highlights and flag important sounds—are pitched as privacy-first, though the press release cuts off before detailing how that data is processed or retained.

For a technical audience, the notable throughline is Apple’s continued bet on on-device silicon (S11, iPhone vision models) to justify always-on biometric and audio capture as a privacy story. Incremental hardware updates round it out: Ceramic Shield 2 glass, 25% longer workout battery, and faster charging. Pre-orders open now with availability September 18.