Apple (AAPL) on Tuesday unveiled two new versions of its best-selling wearable, the Apple Watch. Called the Apple Watch Series 6 and Apple Watch SE, the watches will cost $399 and $279, respectively, when they launch on Sept. 18.

The watches feature a variety of updates designed to appeal to both new and existing Apple Watch customers, and should help Apple continue to grow its Accessories business alongside the incredibly popular AirPods and AirPods Pro.

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The Apple Watch Series 6 is the more premium of the two watches, and is the successor to the Series 5. The watch’s now-iconic design remains unchanged, as it more or less has since the original Apple Watch launched in 2015.

Apple Watch Series 6

The Series 6 will be available in two sizes. A 40mm version will be available for those with more petite wrists or who want a smaller watch face, while a 44mm version will fit on those who have thicker wrists or want a generally large screen size.

The Series 6 will be available in a host of new colors including blue, gold, black, and red.

Inside, the Series 6 features Apple’s new dual-core S6 processor for improved performance and a brighter always-on display, as well as an altimeter.

Apple has also added a new sleep-tracking feature to watchOS 7, the operating system that powers the Apple Watch.

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The feature allows you to monitor your sleep each night, and determine how well you’ve slept by measuring micro-movements picked up by the watch’s accelerometer. Before you head to bed, the watch will also notify you of how much power it has left and, if it’s below 30%, recommend that you recharge it before hitting the sack.

The Series 6 also comes with a new blood oxygen level detector. Built into the underside of the watch, the sensor is able to measure your overall blood oxygen level and notify you if it’s low. Measurements take just 15 seconds, and will record background measurements while you sleep.

Blood oxygen level helps provide you with an understanding of your overall heart health.

The new sensor further pushes Apple into the healthcare space following the release of the Series 5 and its ECG heart rhythm sensor. Healthcare monitoring could prove to be a lucrative area for Apple, and CEO Tim Cook himself has expressed his bullishness for the company’s healthcare efforts in the past.

The company also introduced a new band called the Solo Loop, a silicon loop that is stretchable and lets you easily slip the watch onto your wrist. There’s no clasp or buckle, and it’s available in seven colors and multiple sizes to fit your wrist. A second version of the Solo Loop is also available in braided fabric alongside new Apple Watch Nike loops and Hermes bands.