Guys, I've been wondering about the rumors around heart rate sensors in smartwatches. Do they use electrical signals, reflect light, or monitor pressure changes? What's the technical background here? Can someone explain it in detail?
How do heart rate measurements work in smartwatches?
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This topic is definitely something a lot of people wonder about. I’ve owned a few smartwatches myself, and when I looked into how they measure heart rate, I found that the most common method is photoplethysmography (PPG). Essentially, it works by shining green LEDs onto your skin and measuring how much light is absorbed by the blood vessels underneath. Since blood volume changes with each heartbeat, the variations in light absorption are captured and converted into a heart rate reading. Some premium models, like the Apple Watch Series 6+, also include an electrocardiogram (ECG) sensor, which measures electrical activity directly for more accurate results—especially useful for detecting conditions like arrhythmias.
My old Xiaomi Band only used PPG, and it usually gave me results with 90-95% accuracy, but it sometimes triggered false alarms during sleep. So, if you want truly reliable data, going for a model with ECG support—like the Garmin Venu or Withings ScanWatch—makes more sense. Of course, fit also matters: the tighter the watch sits on your wrist, the better the sensor contact, and the lower the chance of errors.
That's a really smart question, I've always wondered about that too! I've heard that it works with a combination of lighting (LED) and sensors (photodiodes), but is that really the case?
Smartwatch heart rate monitoring typically works using a method called **photoplethysmography (PPG)**. Similar to the oxygen sensor on your fingertip, it uses light to detect changes in blood flow. LEDs shine green light onto your skin, and a photosensor measures the variations in the reflected light to calculate your pulse. It’s a simple but effective method, functioning much like non-invasive monitors in hospitals.
As you know, ECGs measure heartbeats using electrical signals—those are the methods used in medical devices. PPG, on the other hand, is simpler and ideal for everyday use, but it differs by relying on optical signals rather than electrical activity. So, have you noticed the green light on the back of your sensor? That’s PPG in action!