The Apple Watch Series 12 and Ultra 4 offer a range of new health and fitness features. Here's everything that's new.

Apple today revealed the following features for the two new devices:

• New "Health Sensing System": A redesigned sensor architecture with three main improvements, including increased electrode surface area for better ECG skin contact, photodiodes arranged in a ring for more efficient light capture, and larger, more power-efficient green LEDs for accurate heart rate readings during motion.
• Continuous heart rate sensing: Heart rate is now measured every five seconds throughout the day, 60 times more frequently than before, viewable via a new watch face complication.
• Higher-frequency HRV: Heart rate variability is sampled up to 24 times more often, with separate recovery and overall HRV values shown in a new section of the Heart Rate app.
• Daytime vitals view: A new toggle lets users switch between overnight and daytime vitals, potentially catching shifts in metrics before they show up in overnight readings.
• VO2 Max test: A new test has users set up their iPhone to watch them perform a series of exercises, delivering results immediately alongside data from their Apple Watch.
• Most accurate step tracking: A redesigned pedometer model with new machine learning algorithms improves distance accuracy for indoor workouts and all-day step counts.
• Steps complication: A brand-new watch face complication, enabled by the S11 chip, lets users track their step count in real time.
• Longer workout battery life: Up to 10 hours during an outdoor workout, 25% more than the previous model, with 15 minutes of charging now delivering up to 12 hours of extra battery. The Apple Watch Ultra 4 goes further, with up to 50 hours of everyday battery life, 84 hours in Low Power Mode, and a new Max Extended Workout mode rated for up to 45 hours of outdoor tracking; 15 minutes of charging adds up to 18 hours of battery.

The Apple Watch Series 12 starts at $399 and the ‌Apple Watch Ultra 4‌ starts at $799, with pre-orders for both open today and availability beginning Friday, September 18.