Boxym Smart bluetooth 5.1 Fingertip Pulse Oximeter with Android IOS supporton a flash sale for $US19/99 or ~$AUD28.45 posted Lots of very good reviews on the listing with comments.
Specifications :
Brand BOXYM
Material ABS
Color Gray
Weight 42.5g
Size 58 x 32 x 34mm
Connect Method Bluetooth 5.1
Batteries 2 x 1.5V AAA Batteries(Not Included)
Display Mode HD Two-Color OLED Screen
Screen Size and Specification 1.3' QVFA, resolution 320*240 HD OLED
Use Environment Operating Temperature: 5℃~40℃
Storage Temperature: -10℃~40℃
Ambient Humidity: 15% To 80%When Working; 10% To 80% Storage
Atmospheric Pressure: 86kpa~106kpa
SpO2 Measurement range: 70~100%
Resolution: ±1%
Accuracy: ±2% (70%~99%), unspecified (<70%)
Pulse Rate Measurement range: 30~250 bpm
Accuracy: ±1bpm
Perfusion Index (PI) Measurement range: 0~30%
Accuracy: ±1%
Measurement Method Non-Invasive, Continuous Detection Of Arterial Oxygen Saturation And Pulse Rate
Closed Mode 8 Seconds Without Operation, Automatic Shutdown
Pulse Rate Measuring R-ange: 30BPM ~ 240BPM
Measurement Accuracy: ±1BPM Or ±1% Of The Measured Value (Larger Value)
Power Consumption Less Than 30mA
If oxygen saturation is an issue you should probably already be at the hospital? Seems jury out:
https://www.yalemedicine.org/news/covid-pulse-oximeter
Might be of use if you live in NSW.