Ask HN: Which smartwatch is the best in self-hacking/quantified self?

Garmin has always had about the best track record with data accessibility, by far.

Apple Watch is probably a very distant second -- especially now since they've really nerfed the health data exporting. Launch Health app, click on user photo, click "Export All Health Data", wait forever, have "fun" parsing it.

Fitbit's always been a jerk about holding the data ransom for paid membership tiers.

Here’s some docs on the rt1025: https://www.richtek.com/Home/Design%20Support/Technical%20Do...

And a youtube video on their dev kit:

https://youtu.be/rM3a4xL3d50

In the medical/research sphere I would recommend Empatica, but it is quite expensive:

- https://www.empatica.com/en-gb/

Also, recording ECG on the wrist is not ideal. Other alternative placements are the biceps and of course the chest. There are specific sensing devices that measure what you're interested in that cover both locations, but inccur larger cost than Fitbit.

https://github.com/AmuletGroup/amulet-project

This let us build a custom operating system that could run multiple apps and include external sensors via Bluetooth plus a few internal sensors plus a link to a smartphone (and it's sensors). Near the end of the project I had a bunch of them (125 I think) made by an electronics assembly firm. If you want to build your own those files might be a starting point, but I'd also add the warning that many of the components, particularly the nRF51822 radio/MCU are likely no longer available in that exact version (Nordic changes their chip design often) which also means the firmware would need porting to the latest SDK. The touch interface chip is now obsolete. To get 125 built I had to pre-buy all the critical components we needed (some of them off eBay) and send them to the manufacturer. The e-ink LCD panels were hard to find also.

You might be interested in this:

https://hackaday.com/2019/02/20/custom-firmware-for-cheap-fi...

That Arduino IDE generated firmware will run on a variety of cheap fitness trackers from China (the ones that use an nRF52832 radio/MCU). I haven't been active in this area for a few years so there may be new products available now. I see there are a number of self-built smartwatch projects on HackADay:

https://hackaday.com/?s=smartwatch

I'd also warn that getting reliable, accurate medical sensor data from a smartwatch or body worn medical sensor is not a solved problem. Unlike traditional medical sensors used next to a hospital bed a mobile sensor is subject to a lot of motion and environmental changes which messes with the readings. It's difficult to keep a sensor attached to one specific place on a human body. The more advanced sensors you'd like such as blood pressure are not available yet. Heart rate variability in Garmin's is usable, but wrist or body motion can throw it off. A chest strap such as a Polar H7 will give you a much better heart rate and HRV reading, but many people find them uncomfortable to wear. Blood oxygen readings can be fairly accurate when the person is not moving and the strap is tight, but will vary wildly once the person is motion. Be prepared to have to filter the data (e.g., throw out sensor data when the accelerometer indicates motion). Do a search for the new devices promising blood pressure (Samsung I think) or blood glucose monitoring (Apple). One of those might fit your needs when they become available. Beyond that have a look at medical web sites to see what hospitals are using (although those devices tend to require a prescription and are usually only sold to hospitals). You might find some leads here:

https://www.mobihealthnews.com/

There are some research projects in this area too, here's one of the big ones:

https://md2k.org/

led by Santosh Kumar:

https://www.memphis.edu/cs/santosh-kumar/mhealth-systems-lab...

Deborah Estrin has done a lot of excellent research on mobile health sensing as well:

https://en.wikipedia.org/wiki/Deborah_Estrin https://destrin.tech.cornell.edu/

Her Open mHealth project might be useful for making sense of the data you collect:

https://www.openmhealth.org/

You might find some leads from Tanzeem Choudhury's work also:

https://pac.cs.cornell.edu/

though her work tends to use smartphones. Good luck!

What is the best smartwatch that maintains privacy?

I have a Pebble Steel, but it will not sync with Gadget Bridge no matter what settings I try.

Otherwise, I would recommend starting off with a Garmin device. I personally use a Garmin Fenix 6X Pro, which I recommend. There is a new Garmin watch out, with updated sensors, called the Garmin Enduro, however, I do not know how it fares. It just came out within the past few days or so and there are very little reviews on it. I would not purchase a Garmin until you know if the Enduro is solid or not. It should be noted that the oxygen saturation (SpO2) on the Garmin Fenix 6 series can be questionable for some. I personally would not rely on it, but each update makes it better. [No wrist-based SpO2 sensor should be relied on for regular, non-strenuous activities at this point.] Regardless, Garmin derives your respiratory rate through something called the respiratory sinus arrhythmia. It is updated at a high frequency rate, to the point where you would get near-instantaneous alerts, if you set up your own app or configuration. You do not need an ECG sensor for this, and the photoplethysmography (PPG) sensor works great on the Garmin watches, for doing this. An ECG sensor really is not necessarily superior, and there are significant advantages to PPG sensors (like being able to determine the actual blood volume pulse of your capillaries).

Empatica E4 is the holy grail (which I have), but a Microsoft Band 2 (which you can get super cheap on ebay) does pretty much the exact same thing. There is a full working open source API for the Microsoft Band 2 on Github, which works excellently. For what the Empatica E4 is, it is very expensive. You also cannot use it without a direct connection to the internet. Here is a link to the Empatica E4: https://www.empatica.com/research/e4/. In terms of dealing with the internet problem, in my opinion, RADAR-BASE is the best way of dealing with that: https://radar-base.org/.

I also have a Respiban (a chest-worn device with peripheral sensors--but also monitors breathing), which I use in conjunction with the Empatica E4 and Garmin Fenix 6X Pro. But, it is better always to start off with the starter version of the Respiban, the Bitalino: https://bitalino.com/products/plugged-kit-dual-mode-ble-bt

Using my Respiban in conjunction with the Empatica E4, I used machine learning (via journal articles I referenced and re-implemented) to detect stress (both positive and negative) to a 95+% confidence interval. For both the Respiban and the Empatica E4, I utilize Lab Streaming Layer to interface with Machine Learning packages such as Keras.

But, for starting out, either the Garmin Fenix 6 or the Garmin Enduro will be the way to go.