Apple Watch Ultra 4 review: a more accurate heart sensor, 50-hour battery life, and new AI audio features

The Apple Watch Ultra 4 comes with three main upgrades: more detailed heart rate measurement, significantly longer battery life, and a suite of AI-powered audio features. The new health sensor system works with the S11 chip, measuring heart rate every 5 seconds throughout the day and sampling heart rate variability (HRV) 24x more often than the previous generation, separating recovery data from long-term heart health.

Battery is the biggest leap: general use reaches up to 50 hours, low-power mode 84 hours, a 15-minute charge adds 18 more hours, Extended Workout mode tracks GPS for 25 hours, and Max Extended Workout lasts up to 45 hours — enough for a 100-mile ultramarathon. On audio, 4 new features have been added: Sound Recognition, which alerts hearing-impaired users to important sounds like sirens; Live Rewind, which recalls a 15-second conversation summary via a double-press of the Digital Crown; Siri Recap, which captures key points; and Shazam, which identifies music automatically. Apple states no raw audio is stored, with processing happening in the S11 chip's Secure Exclave, which deletes audio immediately after use.

The case remains 49mm titanium, in natural titanium and black titanium, using 45% recycled materials (including 100% recycled titanium). It features a Readiness Score from 0–10 combining exercise, training load, heart measurements, and sleep quality, alongside a redesigned Health app with a Longevity tab comparing Health Age. It runs watchOS 27 with Apple Intelligence-powered Siri and single-hand gesture control. Thailand pricing starts at 29,900 baht ($799 in the US), with pre-orders opening September 10, US sales starting September 18; Thailand's sale date hasn't been confirmed yet.