What the sensors measure, which claims are regulator-backed, and how platform lock-in can switch a feature off.
Updated September 19, 2026
Modern smartwatches list an intimidating array of health sensors. Some are genuinely useful and regulator-reviewed; others are best treated as trends, not diagnoses. And in a twist most buyers never expect, a feature you paid for can be switched off by a legal dispute. Here's how to read the sensor list.
An electrocardiogram (ECG) feature checks the heart's electrical rhythm for signs of atrial fibrillation. This is one of the few consumer health features with a real regulatory pedigree: Apple worked with the US FDA for years to receive De Novo classification for the Apple Watch's ECG app and irregular-rhythm notifications, making it the first direct-to-consumer ECG available over the counter. If clinically meaningful heart features matter to you, look for ones with that kind of clearance rather than a vague wellness label.
For runners and hikers, location accuracy depends on 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 the feature that fixes it.
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 — so a full-smartwatch experience means charging daily, which clashes with sleep tracking. Water resistance is spec'd too: the Series 10 is rated to 50 metres under ISO 22810, i.e. swim-proof but not for scuba or high-velocity water.
The most surprising lesson is that 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. It's a reminder that a sensor on the spec sheet isn't always a sensor you'll be able to use — platform and legal context matter.
This article is original analysis grounded in independently verified references, including non-English outlets. The facts above are sourced so you can check them yourself.