A new comparison of smartwatch health sensors has given the Apple Watch Ultra 2 the edge over some of its biggest rivals. The study by bioinformatics scientist Rob ter Horst (The Quantified Scientist on YouTube), looked at how accurately top wearables track heart rate and sleep.
Heart rate and sleep tracking
For heart rate testing, Horst used a Polar H10 chest strap as the benchmark. The Apple Watch Ultra 2, running watchOS 26 beta, delivered results that were nearly identical to the strap during indoor runs. The Huawei Watch 5 was on par, while others showed more noticeable gaps: the Galaxy Watch 7 came close with about a 3% deviation, but devices like the Garmin Forerunner 570 (7%), Garmin Fenix 7 (9%), and Whoop MG (6%) were less precise.
Outdoors, during running and cycling, the Ultra 2 held its lead, while the Forerunner and Whoop slipped further behind with deviations climbing to 12–15%.
Sleep data was compared against the Hypnodyne ZMax EEG device, which itself is considered around 83% accurate. The Apple Watch Ultra 2 scored 73% for REM and deep sleep, and 86.5% for light sleep. That put it ahead of rivals like the Oura Gen 4 ring, Whoop 4.0, and Garmin Fenix 7.
Takeaway
While this was a single-user test and broader studies would be needed to confirm the results, Horst’s findings suggest the Apple Watch Ultra 2 offers some of the most reliable wrist-based health tracking currently available. Chest straps are still more dependable for weight training, where wrist tension can interfere with readings, but for runners, cyclists, and everyday sleep tracking, Apple’s top watch looks hard to beat.
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