Apple says the Apple Watch Series 12 and Apple Watch Ultra 4 have the most accurate heart rate sensing in a wearable, and it is pointing to a study of more than 1,000 participants run in July and August 2026 to back the claim. The study compared Apple Watch against what Apple calls leading competitors.
The claim rests on the new Health Sensing System, which pairs new optical and electrical heart sensors with larger, power-efficient green LEDs. Apple’s Kaiann Drance, vice president of Worldwide Apple Watch Product Marketing, repeated the phrase in the Ultra 4 announcement, saying the new system and S11 chip deliver “the most accurate heart rate sensing in a wearable.” Our Series 12 preview has the pre-event expectations.
What Apple’s 1,000-person study claims
Apple’s press release gives four facts about the study. Everything else is unpublished.
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| Detail | What Apple has published |
|---|---|
| Participants | More than 1,000 |
| When | July to August 2026 |
| Comparison | Apple Watch versus leading competitors |
| Result | Apple Watch had the most accurate heart rate sensing in a wearable |
| Competitors named | Not published |
| Reference method, activities tested, error figures | Not published |
| Peer review or full paper | Not published |
Without a reference method or error figures, the claim cannot be checked against other wearables today. Apple has not said whether it will release the full study, and the release does not say which watch models were tested or whether the participants wore Series 12 hardware specifically.
What changed in the sensor to support the claim
Apple lists three hardware changes: new optical heart sensors, new electrical heart sensors and larger green LEDs that Apple describes as power-efficient. The larger LEDs are the likely reason the watch can now sample heart rate every 5 seconds all day without cutting into the 24-hour battery rating.
- Heart rate: measured every 5 seconds throughout the day
- HRV: measured every 5 minutes, 24 times more often than before
- Two HRV readings: Recovery HRV for daily stress and recovery, plus overall HRV
- Daytime vitals view, with overnight vitals compared to a personal Recovery HRV baseline
The same sensors and sampling rates apply to the Ultra 4, and Apple makes the identical accuracy claim for both watches.
Why the accuracy claim matters beyond the watch
The new heart data flows into more places than before. The Readiness score uses vitals as one of its four inputs, the new Health app’s Health Age feature pulls resting heart rate and HRV from Apple Watch, and the Longevity tab counts heart health as one of its seven categories.
Apple’s own caveat still applies: the Vitals app is for wellness purposes, not medical use, and the release does not extend the accuracy claim to ECG, blood oxygen or any clinical feature. Series 12 starts at $399 and Ultra 4 at $799, with store availability on Friday, September 18, and the new Health app arrives with iOS 27 on September 14. Our event recap covers the rest of the announcements.
