How do smartwatches measure heart rate and other vital signs, and what sensors are used?

Question

I can understand the heart rate part since watches are worn on the wrist, where our pulse can be determined, though I’m not quite sure, but what about the other vital signs? how? 

In: Technology

Answer 1

Smartwatches use PPG (photoplethysmography) sensors that shine light through your skin and measure changes in blood volume. They can also have ECG sensors to track your heart’s electrical activity. For other vitals like oxygen levels, they use SpO2 sensors that measure blood oxygen saturation. It’s basically a lot of fancy light and sensor tech!