Google has requested FDA approval for Fitbit's passive heart rate monitoring algorithm. The technology was found to detect cases of atrial fibrillation with 98% accuracy in a recent study of Fitbit users. The data was collected using PPG technology built into Fitbit devices.
https://www.notebookcheck.net/Fitbit-s-passive-heart-rate-monitoring-tech-has-been-submitted-for-FDA-approval.610424.0.html