It checks your ECG in the background, and while it won't catch every instance of fibrillation, it could help people who don't even know they have an issue. Apple brought American Heart Association President and cardiologist Dr. Ivor Benjamin onto the stage, and he said the feature could be valuable for certain users. "In my experience, people often report symptoms that are absent during their visits. That is why this information is vital," he said.

Apple also unveiled another interesting but completely different safety feature for the new Watch. Thanks to a new accelerometer and gyroscope, it can detect when you slip or fall. It detects not only your downward motion but also when your arms are flying up in a typically defensive stance. In other words, it's a new, more high-tech version of the Life Call "I've fallen and I can't get up" device.

Watch Series 4 can tell the difference between a slip and a fall, a programming feat that wasn't easy to figure out, said Apple's Jeff Williams. You can set it up to automatically call emergency services and contact your loved ones if you're immobile for at least a minute. It seems like overkill if you're young and athletic, but it could be an extremely valuable feature for the elderly -- or clumsy.

Follow all the latest news from Apple's 2018 iPhone event here!