Retired M.D. (neurosurgical anesthesiologist) here:

Just bought a Huawei Honor 5 watch with pulse oximeter and heart rate functions: numbers seem correct and the device is fast: results in 5 seconds for O2 sat; almost instantaneous for HR.

Compare to Apple Watch HR function which takes at least 10 seconds to show result. Simultaneous side-by-side comparison of 2 devices: near identical numbers.

Even more impressive: Honor 5 costs $33 here: https://www.walmart.com/ip/HUAWEI-Honor-Band-5-Smart-Watch-B...

Superlight, compact, and comfortable. Huawei is no humbug!

Garmin also has them on several devices: https://support.garmin.com/en-US/?faq=SK2Y9a9aBp5D6n4sXmPBG7

Garmin seems to be highly inaccurate at measuring oxygen and the devices take a very long time compared to a finger oximeter. I get 93% but a cheap Walmart finger oximeter shows me at 99%.

Wow they finally did it. After the hardware being there for _years_ they managed to get around to enabling the software. I already jettisoned them for Garmin after waiting so long.

Same frustrations here! Couldn't believe when I bought their smart device based on advertising that said they had the hardware to do it.... but it wasn't enabled.

They didn't really. The UI showing variation while sleeping (with an unlabeled y axis) is the only information that is surfaced to the user afaict.