Thanks to all.
Maybe I’ll pick one up from Amazon... just to have in the medicine cabinet.
On my Samsung phone (6+ years old???) it came with a “health app”. One of the things it does is measure your stress level. Put your finger on the camera light monitor and press the button. It measures your pulse and your O2 level.
They say it is within about 2% of being accurate, so that’s good enough for me. Less than 90%(?) is call the doctor time.
I just did, but returned it, as it was defective and wouldn't register consistent readings.