How do smartwatch heart rate sensors work? How reliable are PPG sensors? Are wearables suitable for use during exercise, or are they only accurate for casual estimates? What’s the accuracy difference between models in different price ranges?
How accurate are smart bands at measuring heart rate?
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PPG sensors work by emitting light and measuring changes in blood flow under the skin. I call them "basa green LEDs" – a simple concept where they track fluctuations in hemoglobin absorption. Their accuracy depends on factors like sensor quality, wrist-skin contact, skin type (light/clear vs. dark/thick), and movement. From what I’ve seen, mid-range models like the Xiaomi Mi Band 7 or Huawei Band 8 have an error margin of around 5-10%, but I’ve noticed the sensor loses track when I move my arm a lot or when it’s cold.
As for use during exercise, they’re reliable but have limits. I use them to monitor my heart rate while working out (like running), and while PPG sensors respond quickly, they’re not as precise as professional-grade devices. Cheap models ($20-30) often give false alarms or skip readings, while higher-end ones (Garmin Venu 3, Whoop 4.0) are more stable. The more you pay, the better the sensor count and algorithm optimization, so premium wearables provide more accurate heart rate, SpO2, and stress level readings.
Come on, measuring heart rate with PPG sensors is like taking the thermometer out of your pocket and holding it to your forehead 😄 Even though they're supposed to be as reliable as "the apple of your eye," the watch starts screaming "Error! Couldn't find heart rate!" the moment you start working out or your wrist gets sweaty. On cheap models, the accuracy is about as trustworthy as a guy trying to count his steps on the way to the café 😅