Apple makes a bold claim for Apple Watch Series 12 and Apple Watch Ultra 4: the new Health Sensing System "delivers the most accurate heart rate sensing in a wearable." Apple backs this with a new study comparing Series 12 to other wearables, including smart rings and fitness bands.

The Health Sensing System is a major upgrade, featuring updated electrical and optical (PPG) heart sensors, new signal processing algorithms, and features like Recovery HRV and the Readiness app.

Apple's nine-page study tested across five sites in the US and Malaysia during July and August 2026. Apple enrolled 1,460 adults, with 1,254 contributing paired measurements. Participants wore Series 12 on one wrist and a competing device on the other, with a Polar H10 ECG chest strap as reference. Comparisons included the Garmin Forerunner 970, Google Pixel Watch 4, Huawei Watch 5, Samsung Galaxy Watch 8, and WHOOP 5. Participants also wore an Oura Ring 5. Tests covered outdoor running, treadmill intervals, cycling, HIIT, strength training, and daily activities.

Apple says Series 12 produced statistically better overall accuracy than every comparison device. Across 159 individual comparisons, Apple Watch achieved statistically better accuracy in 139.

Apple Watch Series 12 is available for pre-order from $399; Apple Watch Ultra 4 from $799. Both launch September 18.