Health sensors
What is ECG on a smartwatch?
ECG (electrocardiogram) is a recording of the heart's electrical activity. On a smartwatch it is done with a single lead: you rest a finger of your other hand on an electrode on the watch for about 30 seconds. Some models cleared by health authorities can detect signs of atrial fibrillation, but it does not replace a medical ECG.
How it differs from heart rate
The heart rate the watch shows all day is measured with light (an optical PPG sensor): it counts beats by watching how blood flow changes in the wrist. ECG measures something else: the electrical signal that makes the heart beat, which shows its rhythm in more detail.
A hospital electrocardiogram uses 12 leads (electrodes on the chest, arms and legs). The watch uses one: it is useful for a rhythm reading, not for a complete study.
How to use it properly
Sit down, rest your arm and stay still during the reading. The watch should fit snugly and the skin should be clean and dry. Movement and poor contact produce readings that are not usable.
Not every watch that shows "ECG" has a function validated as a medical device; on budget models, treat the reading as a reference. If you have symptoms such as chest pain, palpitations or dizziness, see a doctor regardless of what the watch says.
What to check before you buy
- If ECG matters to you, check whether the feature has health authority clearance in your country.
- Make sure the app saves or exports readings so you can show them to your doctor.
- For everyday use, continuous heart rate and SpO2 are usually more useful than an occasional ECG.
Guides to help you choose
Frequently asked questions
No. A single-lead ECG cannot detect a heart attack. If you have chest pain or other symptoms, seek medical care immediately.