What was the first Apple Watch model to include an ECG sensor?

The first Apple Watch model to include an ECG sensor was the Apple Watch Series 4.

Released in 2018, the Series 4 added an electrical heart sensor using electrodes in the back crystal and the Digital Crown. By touching the crown with a finger, a wearer could complete an electrical circuit and record a single-lead electrocardiogram, or ECG. This was different from the optical heart-rate sensor already used by earlier Apple Watch models.

The feature made the Series 4 a major health-focused redesign, alongside a larger display, thinner bezels, a 64-bit S4 chip, fall detection, and redesigned hardware. ECG availability depended on regulatory approval and local rollout, so the sensor’s presence did not mean every owner could use the app immediately in every country.

The common mix-up is the Series 6, which introduced a blood-oxygen sensor, not the first ECG capability. The Series 5 retained ECG, while the Series 3 came before the electrical heart sensor. The Apple Watch ECG feature is intended to help record heart rhythms and support health monitoring; it is not a replacement for professional medical diagnosis.