Good to know regarding the Pulse Oxymeters. I have one, but I will consider it as a quick check device only. That is, if I feel normal and the reading is normal (96 seems to be normal for me), then I’ll be Ok with it.
If you use an oximeter and get a reading in the 50s, throw the thing away. I have one that seems to work pretty good. A dozen years or so ago those devices were selling for hundreds of Dollars. These days they are practically giving them away.
I know that this is going to come across as seeming naive, but these things really should be approved by the FDA. You cannot use them in hospitals unless they are.