What methods are used for heart rate measurement in smartwatches? Are there other technologies besides optical sensors? What factors should be considered to improve the accuracy of health data? How reliable are the results in practice?
How do smartwatches measure heart rate?
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Smartwatches typically use **photoplethysmography (PPG)** optical sensors to measure heart rate. These sensors detect changes in blood flow in the blood vessels near the skin and calculate the heart rate. Additionally, some advanced watches also feature **electrocardiography (ECG)** technology — like mine, though it felt a bit confusing at first, I got used to it later. ECG measures the heart's electrical activity directly, providing more accurate results.
So, what should we pay attention to for better accuracy? It's important to wear the watch on the upper arm, not the wrist, snugly but comfortably. Measurements taken while moving can be misleading — I once got a "heart attack!" alert while climbing stairs, which was obviously wrong. Also, keep the sensor clean, ensure good skin contact, and people with darker skin tones may need to wait a bit longer. In practice, it can be useful for initial estimates in emergencies, but never rely on it for medical diagnosis — even when my doctor said "it's a bit high," I don’t fully trust my watch's reading.
Smartwatch heart rate monitoring largely relies on a technology called **photoplethysmography (PPG)**, an optical sensor method that detects changes in blood flow in small blood vessels near the skin using light waves. However, some premium models also incorporate additional technologies like **electrocardiography (ECG)**, particularly devices such as the Apple Watch, which provide more accurate data through this method. Unlike PPG, ECG measures the heart’s electrical activity directly, offering more reliable results—but this technology is often limited in battery-powered smartwatches.
For accurate readings, the sensor must maintain full contact with the skin, and the arm should remain still during measurements, especially while moving. Factors like skin tone, blood pressure fluctuations, or intense exercise can also affect accuracy. From my experience, data taken during rest at night tends to be very consistent, but measurements during treadmill runs can lag when heart rate spikes quickly. If you're serious about heart health, comparing devices from different brands could be beneficial.