Via Steve Mould on YouTube: The bizarre flashing lights on a smartwatch

Steve Mould just shared a very interesting video explaining how the LED lights on smart watches are able to measure your heart rate (and in some devices, SpO2) through the skin, in human-understandable terms. It's a great sumamry of the complexities involved in quantifying biological data non-invasively with the power of physics.

Worth a watch, go check it out on Mould's channel; though I am a bit sad that my favorite protein in all of the human body — hemoglobin — did not get an explicit shout-out.