5 New Apple Watch Series 12 & Ultra 4 Health Features Explained!
In a Nutshell
The Apple Watch Series 12 and Ultra 4 introduce a redesigned optical heart rate sensor that enables continuous 5-second sampling throughout the day, including during movement, while maintaining 24-hour battery life through the S11 chip’s always-on processor. New dual HRV metrics—RMSSD for short-term recovery and SDNN for broader context—along with a personalized Readiness Score that factors in activity, sleep, and vitals, provide more detailed health tracking. Additional features include a beta Health Age metric that estimates biological age using multiple health data points, with hardware features launching now and the redesigned Health app with Health Age arriving in 2026.
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The sensor layout has been completely changed with a more efficient ring of photo diodes surrounding a new arrangement of green LEDs. These green LEDs are now more power efficient. The watch is now prioritizing green light not only during workouts but continuously throughout the day. Previous Apple watches generally tended to rely more heavily on lower powered infrared light for background heart rate measurements and often waited for relatively clean moments when you were not moving very much.
The Series 12 and Ultra 4 can now use green light to measure heart rate as often as every 5 seconds, including while you are moving. The red lights are still used for SPO2 measurements, though that might not be available in all regions.
This is the most practical important sensor improvement that Apple has introduced. The Apple Watch has always had great heart rate tracking during exercise, but these new improvements are about filling in those gaps between the background measurements and continuing to produce data while you're moving around without starting a workout.
Testing will focus on whether the watches continue reporting reliable heart rate when walking, climbing stairs, carrying around things, or just moving normally without starting an exercise. This is separate from workout accuracy.
The S11 chip has an always on processor that can handle these background tasks without constantly waking up the main processor. This helps explain how Apple can increase heart rate sampling so dramatically while the Series 12 still has a claimed 24 hours of normal battery life.
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