Apple Watch Series 12: a Deep Dive Into Its Heart Sensor
WHO:
9to5Mac - Rob ter Horst from The Quantified Scientist YouTube channel conducted the heart rate sensor comparison.
MacRumors - Apple is the manufacturer of the Apple Watch Series 12.
WHAT:
9to5Mac - The Apple Watch Series 12's heart sensor performed with a correlation of 0.98 during running, with some minor deviations at higher heart rates, and a correlation of 0.97 during weightlifting, which is considered "quite good" compared to other devices tested for weightlifting.
9to5Mac - The Apple Watch Series 12's step counter was tested by manually counting roughly 5,000 steps, and the device was found to be generally accurate or only slightly overcounted.
9to5Mac - The Apple Watch Series 12's heart sensor measures heart rate every five seconds even when the user isn’t active.
9to5Mac - The heart sensor performed with a correlation of 1.0 during indoor cycling, 0.98 during running, and 0.97 during weightlifting compared to a Polar H10 ECG chest strap.
MacRumors - The aluminum models of the Apple Watch Series 12 are available in light gold, dark bronze, black, and space gray, while ceramic models come in pearl white and night blue, and polished titanium models are available in radiant gold and natural.
MacRumors - The Series 12 uses Ceramic Shield 2, which is 60 percent tougher than the Ion-X glass used in previous models.
MacRumors - The Health Sensing System in the Series 12 provides a readiness score based on metrics such as recent activity, vitals, and sleep, which takes about a week of data collection before it starts providing scores.
Ground Truths - Apple announced a revamp of its Health Sensing System, rolling out a Readiness score (0 to 10) and increasing the frequency of heart rate variability (HRV) outputs 24-fold.
9to5Mac - The Apple Watch Series 12 features a revamped heart sensor that measures heart rate every five seconds.
9to5Mac - The heart sensor performed with a 0.98 correlation during running and a 0.97 correlation during weightlifting compared to a Polar H10 ECG chest strap.
MacRumors - The Apple Watch Series 12 has a Health Sensing System that provides a readiness score based on recent activity, vitals, and sleep.
MacRumors - The Series 12 is available in 42mm and 46mm sizes, with pricing starting at $399.
MacRumors - The Series 12 can achieve up to 12 hours of normal usage from a 15-minute charge.
WHERE:
MacRumors - The Apple Watch Series 12 is available for purchase, though specific locations are not mentioned.
WHEN:
MacRumors - The Apple Watch Series 12 was released on the same day as the article's publication.
MacRumors - The Live Rewind and Siri Recap features powered by the S11 chip will be available later this year.
WHY:
Ground Truths - Apple is marketing readiness scores as a measurement of autonomic nervous system health, a digital marker for future disease, and a holistic metric to promote healthspan and longevity.
9to5Mac - The new heart sensor provides detailed insights into how everyday activities affect heart rate.
MacRumors - The updates in the Series 12 are aimed at improving health monitoring capabilities.
HOW:
MacRumors - The Health Sensing System in the Series 12 will adjust the readiness score throughout the day based on metrics such as recent activity, vitals, and sleep.
9to5Mac - The heart rate sensor's performance was tested during indoor cycling, running, and weightlifting.
MacRumors - The Series 12 uses an S11 chip that is faster than the S10 in the previous model.
(UPDATED September 19, 2026 21:56 UTC)
The Apple Watch Series 12 has shown impressive performance with its heart sensor, achieving a correlation of 0.98 during running and 0.97 during weightlifting, which is considered quite good compared to other devices. In addition, the step counter was tested against a manual count of roughly 5,000 steps and was found to be generally accurate, with only slight overcounts. Apple is promoting readiness scores as a new way to measure autonomic nervous system health, with the Health Sensing System adjusting these scores throughout the day based on various metrics like activity, vitals, and sleep.
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(UPDATED September 19, 2026 18:55 UTC)
Apple has unveiled the new Apple Watch Series 12, which features a heart sensor that measures heart rate every five seconds, even when users are inactive. The heart sensor has shown impressive accuracy, with a correlation of 1.0 during indoor cycling, 0.98 while running, and 0.97 during weightlifting when compared to a Polar H10 ECG chest strap. Additionally, the Series 12 boasts a revamped Health Sensing System that provides a readiness score based on various metrics and uses Ceramic Shield 2, which is 60 percent tougher than previous models' glass.
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(UPDATED September 19, 2026 12:58 UTC)
The Apple Watch Series 12 has been released and features a revamped heart sensor that measures heart rate every five seconds, showing impressive performance with a 0.98 correlation during running and 0.97 during weightlifting compared to a Polar H10 ECG chest strap. This new model, available in 42mm and 46mm sizes starting at $399, also includes a Health Sensing System that provides a readiness score based on recent activity, vitals, and sleep, and can achieve up to 12 hours of normal usage from just a 15-minute charge. Additionally, the Series 12 is powered by the faster S11 chip and will introduce Live Rewind and Siri Recap features later this year.