(Duke University) Biomedical engineers at Duke University have demonstrated that while different wearable technologies, like smart watches and fitness trackers, can accurately measure heart rate across a variety of skin tones, the accuracy between devices begins to vary wildly when they measure heart rate during different types of everyday activities, like typing.

Original source: https://www.eurekalert.org/pub_releases/2020-02/du-hrm021220.php