Apple Watch Series 4

After three generations of the same silhouette, Series 4 changed the proportions. Cases grew to 40 and 44 mm while the body got thinner, and the display expanded by more than 30 percent so more of the face was usable for watch complications.

The back crystal now held electrodes that, together with the Digital Crown, formed an electrocardiogram sensor. After a software update in December 2018 it could record a 30-second ECG, which Apple had cleared with the FDA. Fall detection used the improved accelerometer and gyroscope to call for help automatically.

The S4 chip was the first 64-bit processor in the watch and doubled performance, while the Digital Crown gained haptic feedback. Most people saw it as the model where the watch finally became a health device.