https://web.stanford.edu/class/cs231a/prev_projects_2016/finalReport.pdf https://web.stanford.edu/class/cs231a/prev_projects_2016/fin... https://www.forbes.com/

https://web.stanford.edu/class/cs231a/prev_projects_2016/finalReport.pdf https://web.stanford.edu/class/cs231a/prev_projects_2016/fin... https://www.forbes.com/sites/robertglatter/2018/01/30/novel-video-camera-can-monitor-your-heart-rate-using-only-your-face/ https://www.forbes.com/sites/robertglatter/2018/01/30/novel-... Essentially, using appropriate image analysis, they can sense the pulse of blood moving through the skin