Apple unveiled the Apple Watch Series 12 and Ultra 4 with eight new health and fitness features. A redesigned "Health Sensing System" improves ECG and heart rate accuracy. Heart rate is now measured every five seconds, and HRV is sampled up to 24 times more often.

A new daytime vitals view helps spot health shifts early. The VO2 Max test is simpler, and step tracking is more precise with new algorithms. Battery life improves: Series 12 offers up to 10 hours of outdoor workout, while Ultra 4 delivers up to 50 hours normal use and 84 hours in Low Power Mode.

The Series 12 starts at $399, and the Ultra 4 at $799, with pre-orders open today and availability from September 18.