As it turns out, nowadays you can make your own fingertip pulse oximeter using an Arduino microcontroller and an appropriate pulse oximeter sensor module. There’s nothing to be afraid of, so go ahead ...

A pulse oximeter measures both your pulse and the oxygen saturation in your blood. You’ve probably had one of these on your finger or earlobe at the doctor’s office or a hospital.

The difference between fingers is not huge. So it's fine if you are using your index finger. Should one have a pulse oximeter amid this pandemic? "Pulse oximeter does not identify Covid-19.