Smartwatch sensors explained
Short answer: Most smartwatches have an optical heart rate sensor. In our catalog, 248 models list SpO2, 177 list heart rate, 112 list HRV, 85 list skin temperature and 59 list ECG. A sensor in the list tells you the watch has the hardware, not how accurate it is or what you may do with the reading.
Last verified September 26, 2026.
What each sensor measures
Heart rate is measured with light on the skin. SpO2 estimates the share of oxygen in the blood the same way. HRV is the variation in time between heartbeats. Skin temperature is a reading at the wrist. ECG records the heart's electrical signal when you touch an electrode. Other sensors in the catalog include a blood pressure trend and body composition. Every maker names these differently, and every maker sets its own limits on how the reading may be used.
Sensors in the catalog
| Sensor or score | Models listing it | Brands | Approx. rows |
|---|---|---|---|
| SpO2 | 248 | 36 | 0 |
| Heart rate | 177 | 34 | 0 |
| HRV | 112 | 14 | 0 |
| Skin temperature | 85 | 14 | 0 |
| ECG | 59 | 12 | 0 |
| Readiness score | 45 | 9 | 0 |
| Sleep apnea | 28 | 7 | 0 |
| Blood pressure | 12 | 3 | 0 |
| Blood pressure trend | 6 | 3 | 0 |
| AFib | 5 | 2 | 0 |
| Body composition (BIA) | 5 | 2 | 0 |
Models that list ECG
| Model | Brand | Battery, as listed | Phone compatibility | Release year |
|---|---|---|---|---|
| Apple Watch Series 12 | Apple | Up to 24 hours (10 workout hours) | iOS only | 2026 |
| Apple Watch Ultra 4 | Apple | Up to 50 hours · 84 hours saver | iOS only | 2026 |
| Galaxy Watch 9 | Samsung | Up to 30 hours (AOD) | Android only | 2026 |
| Galaxy Watch Ultra2 | Samsung | 800mAh · up to 4 days | Android only | 2026 |
| Garmin Fenix 9 | Garmin | Up to 29 days (51 mm) | iOS and Android | 2026 |
| Garmin Fenix 9 Pro | Garmin | Up to 31 days · 57 days (solar) | iOS and Android | 2026 |
| Garmin tactix 8 Cerakote Edition | Garmin | Up to 29 days | iOS and Android | 2026 |
| Huawei Watch 6 | Huawei | Up to 4.5 days · up to 11 days in battery saver mode | iOS and Android | 2026 |
| Huawei Watch 6 Pro | Huawei | Up to 4.5 days · up to 11 days in battery saver mode | iOS and Android | 2026 |
| Huawei Watch D3 | Huawei | 6 days (approx.) | iOS and Android | 2026 |
| Huawei Watch GT 7 Pro | Huawei | Up to 12 days · 21 light-use | iOS and Android | 2026 |
| OPPO Watch X3 | OPPO | Up to 5 days · up to 16 days in power saver mode | Android only | 2026 |
| OnePlus Watch 4 | OnePlus | Up to 5 days · up to 16 days in power saver mode | Android only | 2026 |
| Pixel Watch 5 | 30 hours (41) · 40 hours (45) | Android only | 2026 | |
| Apple Watch Series 11 | Apple | Up to 24 hours | iOS only | 2025 |
Showing 15 of 59. Open the full list on the all-models page.
How to read a sensor listing
A listed sensor means the watch can collect that reading. It does not mean the reading is a medical measurement, and many makers say their readings are for wellness only. Regulation and approval differ by country and by feature, so check the maker's own statement for your country.
What to check
Does the sensor need a special band position or a still wrist? Is the result stored in the maker's app or on your phone, and who can see it? Does it need a subscription, see subscriptions explained? Does it work with your phone, see phone compatibility? For recovery-related sensors see sleep and recovery features.
What these sensors cannot do
They cannot replace a professional. If a reading worries you, speak to a health professional, and do not use a watch to decide on treatment.
Before you buy
Check the maker's current details for your model. Features change with updates. See our methodology.