The Health Sensing System is the headline change inside Apple Watch Series 12 and Ultra 4, and it arrives with a specific accuracy claim, a named study, and several notification features whose scope is easy to overstate. Apple’s own press release and specification pages set the actual boundaries on what it measures and what it does not.
This article reports what Apple has published about each feature and what Apple says it does, not what a reader should do with any result the watch shows. Nobody outside Apple has tested this hardware yet, so every figure below is Apple’s own.
| Sensor or feature | On Series 12 and Ultra 4? |
|---|---|
| Third-generation electrical heart sensor | Yes |
| Always-on optical heart sensor | Yes |
| Blood Oxygen sensor | Yes |
| Temperature sensor | Yes |
| ECG app | Yes |
| Hypertension notifications | Yes |
| Blood pressure sensor | Not listed |
| Blood glucose sensor | Not listed |
Does the accuracy claim cover older Apple Watches, or only the new ones?
Apple ties its “most accurate heart rate sensing in a wearable” claim to a study of more than 1,000 participants conducted in July and August 2026, against what Apple describes as leading competitors. Apple’s release frames the claim around the redesigned sensor hardware specifically: a third-generation electrical heart sensor, an always-on optical heart sensor, and larger, more power-efficient green LEDs, all new to Series 12 and Ultra 4. Apple has not stated that the same claim applies to Series 9, 10 or 11, which use the earlier sensor design.
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Does Apple Watch measure blood pressure or blood glucose?
No. Apple’s sensor list for both watches names an electrical heart sensor, an optical heart sensor, a Blood Oxygen sensor, a temperature sensor, a compass, an altimeter, an accelerometer, a gyroscope, an ambient light sensor, a depth gauge and a water temperature sensor. A blood pressure sensor and a blood glucose sensor appear on neither list. What the Health Sensing System adds instead is hypertension notifications and an ECG app, which Apple describes separately from a direct blood pressure reading.
What do hypertension and sleep apnea notifications actually tell you?
Apple names both features in its Series 12 and Ultra 4 material, listing them alongside the ECG app, the Blood Oxygen app and sleep score, without describing the underlying mechanism in the release itself. Apple presents them as notifications generated by the Health Sensing System, not as a diagnosis, and Apple’s own pages are the only source for what either feature is called and does. Apple has not published sensitivity or accuracy figures for either notification type in the material reviewed for this article.
Who is the new perimenopause and menopause tracking built for?
This feature lives in watchOS 27’s Cycle Tracking, not in the Series 12 or Ultra 4 hardware, so any Apple Watch that receives watchOS 27 gains it, not only this year’s new models. Apple’s own description: notifications when cycle changes suggest perimenopause, for users 40 and older, plus postmenopausal bleeding notifications. Apple states the feature is “not in all regions” without naming which regions are excluded.
Does Apple break the accuracy claim down by skin tone or heart rhythm?
No. Apple’s release describes the 1,000-participant study only in aggregate, as a single accuracy comparison against leading competitors. Apple has not published separate results for different skin tones, for people with irregular heart rhythms, or for any other subgroup, in the material it has released so far for Series 12 and Ultra 4.
What Apple has not said
- Which specific products the 1,000-participant study compared against, beyond “leading competitors”
- Which regions are excluded from perimenopause and menopause notifications
- Sensitivity or accuracy figures for hypertension and sleep apnea notifications
- Any breakdown of the accuracy study by skin tone, heart rhythm or age group
Until Apple publishes a fuller methodology for the study or a support document detailing notification accuracy, the feature names and sensor list above are the full extent of what Apple has said. As of September 12, 2026, both watches remain on track for the September 18 in-store date.
