Enlarge / Apple Watch Ultra. (credit: Apple)

CUPERTINO, Calif.—The third and final new Apple Watch introduced at Apple's hardware-reveal event today is the company's first stab at a premium, trail-ready piece for your wrist: the Apple Watch Ultra.

Apple COO Jeff Williams described the new model, which starts at $799 and can be ordered starting today, as an option for "exploration, adventure, and endurance," and its features seem designed for the highest hikes and deepest dives. The Apple Watch Ultra includes deep water resistance (it's EN13319 certified), a siren that can be heard up to 600 feet away, and high-end physical materials. The 49 mm case is composed of "aerospace titanium," while the new "alpine loop" wristband combines titanium with woven fabric.

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  The new action button.

Apple says that in regular use, the Watch Ultra will last for "up to 36 hours" on a single charge, thanks to the "biggest battery yet" on an Apple Watch. That battery life could grow to as much as 60 hours via a "battery optimization setting coming later this fall." The lower-power mode will be achieved via "reduced frequency of GPS and heart rate readings." The Ultra's display is also the brightest yet for an Apple Watch, reaching up to 2,000 nits of brightness—though we're still waiting to hear how battery life will be affected by constant use of max brightness.