Apple Watch Series 9

It may depend on skin type, body composition and wrist hair - perhaps the validation work used a skewed sample? I’ve found the sensor to give stable results, with repeated measurements always within 2 percentage points. And the results give qualitatively very reasonable data when I sleep at high altitude. The readings have a clear dependence on the elevation. I haven’t cross checked against other meters, but my Apple Watch 9 sensor gives stable and reasonable results that match expected altitude trends. So yeah it may not be tuned to a wide enough variety of wrist types.

I love cycling with my apple watch, its actually the largest use case for owning one in my opinion. If I'm not exercising I don't wear it, I like getting the heart rate states synced to strava.

My sleep tracking works pretty well on my S9. It isn't perfect and there are glitches and bugs I've noticed, but overall the long term trend tends to even out and feels pretty comparative to my old Fitbit.

Yes, thanks for asking. Continous Glucose Monitors (CGM). That used to be a diabetic-only problem until Abbott, Dexcom,and other vendors expanded their markets beyond diagnosed diabetics into pre-diabetes markets and exercise, health, and well-being applications like: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10635370/ and: https://www.levelshealth.com/ This has exploded beyond the hundred years of ketogenic research and as research on glycemic variability in mental health has grown. My current kit includes an Apple Watch series 9 and an iPhone SE. Prior to that it was Google Pixel and a Fitbit Sense, though direct BTLE->Watch was not an option in that generation. I have two complications: Abbott Freestyle Libre 3 and Dexcom G7. Continuous Glucose Monitors (CGM). The Dexcom is entirely proprietary. The Abbott is accomplished via a series of 3rd party hacks: https://www.youtube.com/watch?v=YqUZjXo5VXY I'd say open source, but I'm not certain that every link in the chain is open source. I've run many generations of various open source tools on Android and iPhone since no vendor ships a complete end-to-end solution that is perfect. Nightscout and watchdrip are two open source examples: https://nightscout.github.io/ https://watchdrip.org/ When G7 originally shipped last year, sensor data left the sensor and used the iPhone as a proxy-to-cloud storage, as has become the default mode across many IoT devices because it was easy, obvious, despite the unintended consequen…