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The Series 4 marks another major upgrade to the Apple Watch. Here the changes are more cumulative -- the first thing you'll notice of course is its bigger OLED display with thinner bezels, matched to 40- and 44-millimeter sizes. This allows watchOS to squeeze more detail into some screens, and indeed a new Infograph watchface can fit up to eight complications. The digital crown has been re-engineered to include haptic feedback, "clicking" as you scroll. More importantly it's part of Apple's new electrocardiogram (EKG) technology, the other components being a ring around the optical heart sensor and a watchOS app coming later in 2018. By holding a finger on the crown for 30 seconds, the app will be able to detect whether you have a regular heart rhythm or it shows signs of atrial fibrillation. Some other health-related improvements include fall detection, which will pop up an option to call emergency services or even make the call automatically after 60 seconds. The Watch's Emergency SOS function will dial 911, notify emergency contacts, share your current location, and pop up your Medical ID information for providers. Further upgrades include a faster S4 processor, a 50 percent louder speaker, and a relocated microphone for reducing echo in phone calls or Walkie Talkie.