How accurate is the pulseOx?

Ok 

My garmin watch says 85% and my Samsung gs9 says 97%

Check it on a good quality smart phone. You probably don't have sleep apnea. 

Garmin really need to up their game.

C.sco said:

I don't have another pulse oximeter to test it against

Probably it is better to compare with a medical device before say that your is ok. I tested more times with my Fenix 6 Sapphire and my wife one and the data is not alligned with medical devices, unfortunately. 

My Fenix 6X Pro is terrible on taking Pulse OX Readings.  When it does its always low by 4-6% compared to a new finger tip Pulse Oximeter. It also does not track sleep, nor pulse accurately.  Spent a lot of Money for something worse than Fitbit for tracking pulse and exercise.

1. For me SPO2 function it’s useless. I check now the spo2 value with the each at the level of heart and I have had a 87% and on pulsoximeter the value was 98/99. All the time when I checked the value of the SPo2 on my watch was with at least 5  % points below the pulsoximeter.

Same here. 90-94% while medical device reporting 97% and above. Tight fit, no ambient light. Hairy hand.

Its not very accurate and sometimes it needs very long time to measure

i bought a medical device and compared both, my Fenix shows lower (not much but 2-3% could be important if you are at 90-95% range).

During measurement I wear my F6 above the wrist bone and I keep it tight. I have no hair and my skin tone is normal so I think its related to watch accuracy not me.  

I think they are not using the same technology since medical oximeter transmits a red light from the upper led through the fingure which is captured from the lower photodetector sensor so this could not be done the same with Fenix.  

My second watch has better readings