Why are there two green lights on the bottom of my watch?
There are two green lights on the bottom of my watch that come on every so often. Why?
Apple Watch
Hi
These are used by the heart rate sensor. You should not typically notice them working under normal operation (when wearing your watch snugly on the top of your wrist).
More information:
Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support