Same here. You can get a fitness band that measures SpO2 among other things for 30 bucks or so

Most recent Samsung Galaxies have one built in. You just need to enable it in the Samsung Health app.

I have a Samsung Galaxy myself but it's less accurate than a real medical device. Readings depend on how you hold your finger against the sensor.

I think you'd only be looking for a significantly low reading anyway. So if you get a low reading try again until it goes up or it's time to go to the hospital.