On my Samsung S7 phone, I have the Samsung Health app. An earlier version allowed for individually checking pulse and Oxygen Saturation Levels.
I mentioned this to my PCP I think 3 years ago, and he asked me to show it to him. I took the measurement and then he used his finger thingee (nice tech term). He found that amazing and suggested I regularly test myself, which I was and continue to do.
New PCP this year and I mentioned it to her. OSL was spot on and pulse was off by either two or three counts (could have been from her holding my hand, errrr wrist
). She was likewise impressed. IMHO, it is a great app, and has far more features.
Dave