Smartwatch health sensors explained: ECG, SpO2 and GPS
What the sensors measure, which claims are regulator-backed, and how platform lock-in can switch a feature off.
By the Let’s Compare Editorial Team · 1 min read · Updated September 24, 2026
Smartwatch spec sheets now list an intimidating array of health sensors. A few are useful and regulator-reviewed; others are better read as trends than diagnoses. And a feature you paid for can even be switched off by a legal dispute.
Common smartwatch health sensors
| Sensor | Measures | Note |
|---|---|---|
| Heart rate | Pulse | Universal |
| ECG | Heart rhythm (AFib) | Regulator-cleared on some models |
| SpO2 | Blood oxygen | Can be disabled by patent disputes |
| Multi-band GPS | Location | Best accuracy in tough terrain |
ECG: the regulator-backed one
An electrocardiogram (ECG) feature checks the heart's electrical rhythm for signs of atrial fibrillation. It's one of the few consumer health features with a regulatory pedigree. Apple's ECG app and irregular-rhythm notifications went through the US FDA's De Novo review, and the ECG app became the first direct-to-consumer ECG available over the counter. If clinically meaningful heart features matter to you, look for that kind of clearance rather than a vague wellness label.
GPS: go multi-band
For runners and hikers, location accuracy comes down to the GPS hardware. Multi-band (dual-frequency) GNSS is the meaningful step up. Independent testing by DC Rainmaker found it delivers industry-leading track accuracy, especially in tough terrain like cliffs and forests where signals bounce. If your tracks look messy among tall buildings or trees, multi-band is what fixes it.
Battery, water and lock-in
Be realistic about battery. Apple officially rates the Apple Watch Series 10 for up to 18 hours, and that figure already assumes a light day. A full smartwatch experience means charging daily, which clashes with sleep tracking. Water resistance has a spec too: the Series 10 is rated to 50 metres under ISO 22810, so it's fine for swimming but not for scuba or high-velocity water.
Then there's the surprise. Features can disappear. After losing a patent dispute with Masimo, Apple disabled the blood-oxygen (SpO2) sensor on new Apple Watches sold in the US via a firmware update. A sensor on the spec sheet isn't always one you'll get to use, so platform and legal context count too.
Related explainers
- Why some smartwatches last a day and others last weeks
An Apple Watch needs charging nightly; a Garmin can go weeks. The screen and the software explain most of it.
Sources & further reading
The facts and figures in this article come from the references below (some of them not in English), so you can check them yourself.
- ECG app and irregular-rhythm notification — Apple Newsroom
- Fenix 7 Pro multi-band GNSS accuracy in the field — DC Rainmaker
- Apple Watch Series 10 — Apple
- Los últimos Apple Watch se quedan sin SpO2 — Xataka (ES)