Series 4 -

Uses an improved accelerometer and gyroscope to detect hard falls.

Over 30% more screen area with rounded corners. Series 4

The Digital Crown added mechanical-feeling clicks for precise scrolling. Uses an improved accelerometer and gyroscope to detect

Automatically calls emergency services if you are unresponsive after a fall. Series 4

While it no longer receives the latest watchOS updates, the Series 4 is credited with saving the product line. By prioritizing and screen real estate , Apple moved away from being a "mini-phone" on the wrist and toward being a life-saving tool.