Heart rate accuracy on smartwatches has always been the elephant in the room. Most wearables are fine, but fine isn’t good enough when athletes are making training decisions based on the data. Apple is taking a direct swing at that problem with the Watch Ultra 4, and the numbers behind it are hard to ignore.
Apple announced the Watch Ultra 4 on September 9, with pre-orders open now and availability starting September 18. It comes in natural and black titanium, and it runs on the new S11 chip paired with what Apple calls the Health Sensing System, a redesigned set of optical and electrical heart sensors. Apple says a study across 1,000+ participants confirmed it beats other leading wearables on heart rate accuracy. Bold claim, but at least they ran the study.
What the Health Sensing System actually does
The big shift is measurement frequency. Heart rate now reads every five seconds all day long, and HRV is tracked up to 24 times more often than before. Apple splits HRV into two types: recovery HRV for daily stress signals, and overall HRV for broader cardiovascular trends. There’s also a new daytime vitals view so you’re not waiting until morning to spot something off.
Readiness: useful feature or just another score?
The new readiness feature gives you a daily 0-10 score and one of four plain-English recommendations:
- Recover
- Pace Yourself
- Ready
- Go For It
It pulls from sleep, training load, recent activity, and vitals. The algorithm was built with data from Apple’s Heart and Movement Study alongside exercise scientists. So it’s not just vibes. It updates through the day too, which is the part that actually matters for real training decisions.
Battery life that finally makes sense
Everyday use gets you over two days, up to 50 hours. Low Power Mode stretches that to 84 hours. For outdoor workouts with GPS on, you get 45 hours. And 15 minutes of charging adds 18 hours of life back. For a watch at this price point, that’s where it needed to be.