Coronavirus and blood oxygen levels

[Physician-friends, feedback invited!]
We just ordered an oxygen meter for (possibly) early diagnosis of coronavirus. See:
COVID-19: Home Pulse Oximetry Could Be Game Changer, Says ER Doc

This from a scientist-friend (non-physician) who first suggested it:
Here’s the article that talks about low oxygen preceding breathing trouble
The Infection That’s Silently Killing Coronavirus Patients

Here’s one with an interview with the same physician where he mentions GermanyA German Exception? Why the Country’s Coronavirus Death Rate Is Low

The very first paragraph of this one refers vaguely to “a blood test” in Germany given to patients 5-6 days into their illness. By piecing various things together, one can infer this blood test is for blood oxygen levels

A German Exception? Why the Country’s Coronavirus Death Rate Is Low