I've been generally disappointed with my Apple Watch, though it looks good and the fitness tracking app mostly works as intended. I find the interface buggy and slow and you can never use it more than a day in a row without charging.

Before I was gifted a Apple Watch, I bought a cheap Amazfit band (= Xiaomi's band, you can never tell which one is the rebranded one), as they have an API you can get access to, but it doesn't really work that well in practice. I never got approved for the dev API and the reverse engineered API[0] doesn't return all the data either.

In the end I resorted to storing all the data in the Health App and using an app[1] to export the data as a CSV file and push it to my server. The benefit of using this approach is that then the actual device does not matter and you can use whatever fitness tracker you want.

If you are on android, you can use apps like Gadgetbridge[2] and FitoTrack[3] to achieve something similar with some of the Chinese bands. But, I am not sure about how to auto export

[0] https://korniichuk.medium.com/export-xiaomi-data-87f7e284b37... [1] https://www.healthexportapp.com [2] https://gadgetbridge.org [3] https://codeberg.org/jannis/FitoTrack

Prob not fitting your criteria but the Withings band does interesting things like detect when my night time heart beat is high and reasonably guesses that I have a fever. Which I do. I have the BP monitor and scales as well and they work well together but it's the band that as seems to reveal the most insights.

An argument against whoop or any niche bands:

I went abroad for a semester to a country where getting stuff mailed was a PITA. Turns out I lost my whoop charger in my quarantine hotel. Support sent a new charger but to actually mail it was close to impossible.

Now I use an Apple Watch. If I lose the charger basically any city on Earth has a store selling apple products (doesn't have to be a real Apple Store) and I get can a new charger in the same day.

I'd love to hear if anyone has suggestions with an additional feature:

- No internet access / sign up / data syncing to the cloud is required (ideally it wouldn't exist at all). The ideal would be connecting the device directly to a computer via USB or bluetooth and pulling the data / logs off of it directly.

Combined with open data access / reverse engineering this would be very powerful. Basically I want a band where it is impossible for anyone besides me to get access to my data (without physically stealing the band or hacking my computer).

Polar and Suunto were like this in the 90s and 00s.

And they offered fancy features for the time such as VO2max or EPOC.

I wonder if any of their models still work well without apps?

I used to have a FitBit that I wasn't entirely happy with. After some health issues, I recently upgraded to a FitBit Charge 5 that I'm mostly satisfied with. It was quite inexpensive; I got mine for $99. It does continuous heart rate monitoring, but I have doubts about the accuracy of its resting heart rate calculation. It has all of the "interesting sensors" you listed, but I haven't explored them all. The one feature that decided me was the ElectroCardioGram (ECG) function. It's not perfect. It requires that you sit very still for 30 seconds with thumb and forefinger grasping the sides of the FitBit, and it only checks for A-Fib (Atrial fibrillation), but there aren't that many fitness bands that have that function, and it was important to me to get one with that feature.

My biggest disappointment with this band is the sleep tracking (which was also a failing with my previous FitBit). I have to get up at 7:30 to feed my cat, then I go back to bed for an hour or so. Both my old and my new FitBit record 7:30 as the end of my sleep period; they ignore the sleep time after 7:30. I'm also not convinced that a band you wear on your wrist can accurately track REM sleep.

I use the FitBit app for some other features and controls, but I have no idea about "Open data access, reverse engineered APIs, 3rd party data analysis apps".

All in all, I'm happy with my FitBit Charge 5, and I think it's a good value for its price.

Wow, interrupted sleep every day is not good. Maybe auto-feeder once a day would help?

My cat is quite insistent. You really don't want to cross her!

Rem sleep is typically measured in a sleep lab with many sensors, including EEG sensors - which do not exist on the wrist devices; inferring Rem is thus difficult. To me, it's just a kind of "relative" reading: think "rest state", and I care about it changing from time to time.

I upgraded to a Charge 5 from Charge 4, even though I happen to own an iWatch as well. Big mistake.

Charge 5 is happy to beep sms (morse code) from time to time when my cell phone picks up text messages. In the day time, that's fine, buf 4am in the fucking morning? There's no damned way to turn it off.

I am not aware of a skin temperature reading on it, though it does do an EKG-like reading, just like the iWatch. No clue whether it will phone 911 if my ticker gets funky; iWatch is known to do that.

I think I'd rather go back to a Charge 4, if only to get rid of text messages. I really don't need them - especially in the middle of the night.

You mentioned body temperature twice, so I’m going to pick on that one. If it’s a wrist-based device, it’s going to measure your wrist temperature, which normally differs from your body temperature a great deal. The Oura ring works roughly the same with your finger.

What exactly are you looking for WRT your body temperature? Because for most fitness wearables, you just going to be able to log deltas. Kind of a solution looking for a problem at this point.

Overall, you should have well-defined goals before you purchase because a device that can log a bunch of body telemetry gets boring pretty quickly without solid goals.

Makes sense. Could a fever still be detected with the wrist temperature? I was reading the wikipedia page on fever, and it has this interesting graphic showing different fever patterns: https://en.wikipedia.org/wiki/Fever#/media/File:Fever_Patter...

...so naturally I was wondering if this could lead to rough diagnostic method using a temperature sensing fitness wearable.

It's not slim or a fitness band, but I like my Garmin smart watch (the discontinued Forerunner 645 Music). It also doesn't have great data access.

It's comfortable, has good enough battery life, is easy to use, and so on.

Trying to return my Fitbit Versa 3. It drifts about 5 minutes per day :-(

Is it connected to wifi? I would assume that for many of these devices it's cheaper to sync the clock over the internet than to include a realtime clock

Thanks. I am trying the wifi connection to see if this helps.