[wkat4242]

Yeah finger clamps shine through the finger completely. They don't use reflected light.

They are much more accurate for this reason but also more annoying to wear. I think the only daily-wearable one that works this way is the Oura ring.

I'm surprised how well it still works on a watch though. I never tried Apple's implementation as I don't have an apple phone to pair it with, but my galaxy watch 6's SpO2 works pretty decently compared to a finger clamp one, considering it is much harder to do it on the wrist.