PPG is a technique that has been used in healthcare to track the heartbeat since 1972, and it’s been proven to be effective for heart rate variability (HRV) analysis. Note that HRV measurement is not an electrocardiogram (ECG) recording, and it can't be used as a substitute for ECG or a medical check-up.

PPG is used in pulse oximeters, and can also be found in many wristbands and fitness trackers.

When your heart beats, blood flows in and out of the capillaries in your finger. These changes in blood volumes make the tissue in your finger change color.

The point of PPG is to track these changes with the help of light or infrared radiation. We do this through your phone’s camera: the flash illuminates the tissue in your finger, the camera takes a video of the changes, and the result is a short clip of your heartbeat.

Research shows that measurements taken with a smartphone camera are just as accurate as those taken with heart rate monitors. 

But we actually ran our own study, in which we showed that Welltory’s PPG-based phone camera measurements are equal to measurements taken with Polar chest straps, which are ECG-accurate

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