You can buy a cheap smartwatch that will monitor your pulse, give you a pulse oximeter reading, handle text messages and phone calls, take photos, and also within a reasonable margin of error check your blood sugar for about $35 on AliExpress.
What do you mean with that? Depending on the recency of your device they can be quite accurate. I use a Garmin though because they last longer on battery and are a bit more oriented towards sports and health. Some studies I found back then suggested Garmin is not that far off lab testing on most metrics. Yes even the guestimated ones like vo2max.
I mean what I said. There's a reason it's in their manual. And it's not in the back of the "legally cover our butts'" section. It's right next to the description of the feature itself
You'd have to look up the manual specific to your device, just google 'm. Generally it's right next to the explanation about the feature where it tells you it's not suitable for using it to collect health data for any purpose other than that it's fun