watchOS 5 is the fifth release of watchOS, shipped September 17, 2018, with the redesigned Series 4. Walkie-Talkie brought push-to-talk voice over any connection; workouts learned to detect themselves (start and end reminders, automatic pace alerts, yoga and hiking types); and the Series 4's health hardware switched on across the cycle — fall detection at launch, and the ECG app with atrial-fibrillation notifications in 5.1.2 that December, the watch's leap into regulated medical territory.

Walkie-Talkie; automatic workout detection; competitions; Podcasts on the wrist; Siri Shortcuts and raise-to-speak (no "Hey"); web content viewing; student ID cards; and the ECG app/AFib notifications (5.1.2, Series 4).

The ECG clearance made the Apple Watch a medical device in the public mind — saved-my-life stories became a genre — and set the template of hardware shipping ahead of its software switch-on. Walkie-Talkie stayed a beloved niche; the health turn stayed the strategy.