For Apple to continue selling the most popular smartwatch — and the most popular watch — in the world, it will need to get consumers in on advancing personal health technologies, not just communication.

The company has taken pains to redevelop the Apple Watch for its fourth series. The displays push closer (but not right up to) to the edge of the case, matching its curves. They’re more than 30 percent larger than previous versions, but with slimmer 40mm and 44mm profiles rather than 42mm and 46mm sizes. The digital crown and single tactile button remains on the right side of the case.

Like cellular variants of the Series 3, cellular variants of Apple Watch Series 4 will connect to LTE and GPS satellites as well as the standard Bluetooth 5 and Wi-Fi. The edges and rear side is made of black sapphire glass for improved reception. The speaker is louder than ever and the microphone has been placed diametrically afar from said speaker.

A new 64-bit dual-core Apple S4 processor is equipped with a new GPU. A new accelerometer has greater dynamic range and the gyroscope can take data at eight times the rate of previous models. Both components will generate enough data to detect if its user has taken a fall, a trip or a backwards slip using trajectory patterns. SOS mode will activate in the wake of a fall, allowing the user to make a call to emergency services or, if the user is immobile for one minute, automatically start a call.

Apple Watch ECG

The heart rate monitor is back in the rear, but in addition to an optical sensor, there is now an electrode array in the digital crown to produce electrocardiograms — endorsed by the American Heart Association and approved by the Food and Drug Administration. Other tinkering in hardware and software has allowed for two other new features: a low heart rate alert, arrhythmia or an atrial fibrillation alert, also FDA-approved. Data is encrypted in iCloud and can be shared with doctors at the patient’s will.

watchOS 5 gets a big watchface with four complications in the cardinal quadrants inside an analog clock, four in the negative space corners and calendar notifications and reminders lining the actual clock circle itself. New complications from Qantas and LifeSum are also available as well as new meditative “Breathe” visualizations and live action watchfaces featuring elemental actions like vapor or flames. For those already with Apple Watches, expect this big software update on September 17.

Apple Watch Series 4 is rated for 18 hours of general use and 6 hours of workout tracking.

The case comes in silver, gold and space gray and bands are available in gray, black and gold stainless steel. The Apple Watch Nike+ experience is also available through Series 4 and there’s a reflective woven loop. Apple Watch Hermes is also coming with new bands and watchfaces soon.

A standard Apple Watch Series 4 device, available in 24 regions, starting at $399. In 16 of those regions, 34 carriers will have the cellular version from $499. Apple Watch Series 3 will still be available at a new beginning price of $279 starting today. For Series 4, pre-orders can be made from September 14 orders with shipments from September 21.