Device Biometrics - Page 1
Forum section: electronics / testgear

author: metrologist
author_rank: Super Contributor
timestamp: March 13, 2019, 01:37:35 pm
content: It is really a fitness ring, but I am curious how this device detects certain things, like when I sleep. I mean it is amazing how accurately it knows when I sleep. Now I'm sure we've all had the experience of being in a long boring class lecture and you dose off, and catch yourself as your head starts to nod. This little ring knows it. Somehow it knows the difference between three different sleep statesFor example, this is last night's plot, fairly typical. I usually watch 10pm news and soon after I nodded off. I woke up and got ready for bed. I slept unbroken as I recall, and I slowly came to my senses as I woke. I really wanted another hour of sleep, but gave it up there at the end of the plot. It wasn't gonna happen. I started thinking of a Toradex SBC I found in the refuse and forgot to try it out the night before (it works!).It gives more data such as heart rate plot, heart rate variance, and body temperature. Those don't seem too difficult. But then there is respiratory rate. How can a ring on my finger know that? The activity metrics seem easy too, but being out on the hand seem less accurate. It is further just amazing this all happens in such a tiny package, and it can log a month of data and run for a week on a single charge.

author: 0culus
author_rank: Super Contributor
timestamp: March 13, 2019, 01:43:59 pm
content: I suspect some of the `magic' is actually heuristics, based off of the things it can measure directly. Could be wrong though...

author: metrologist
author_rank: Super Contributor
timestamp: March 13, 2019, 01:51:48 pm
content: I guess it could all just be fakery too. I mean, if the ring doesn't move for a certain time, then it assumes sleep. I cannot imagine what sort of sensor could detect such a thing, but it seems to match up so well with my perceptions.I'll have to think of a way to expose it, such as download the data right after I've nodded off and see if it shows any sleep time. It does not give live updates.It doesn't record data if you're not wearing it, it knows that too. It might be neat to figure out how to fake that (conduction, temp, pulse, or?). It looks like it has a few gold contacts and some sort of dark blob that might be an optical type of sensor.

author: DaJMasta
author_rank: Super Contributor
timestamp: March 13, 2019, 05:55:38 pm
content: Heart rate sensors are usually optical, then with an accelerometer you can infer a lot. Sleeping isn't totally still, generally, but is definitely lower activity, prolonged stillness, and lower heart rates, so it wouldn't be hard to infer it based off of generalized data about activities. The motion measurements are probably the biggest part, but if it had access to other data, you can do a number of checks on the inferences you're making to verify them (if the device thinks you're asleep and then you do something on your phone that's associated with it, if it has that data, it knows you aren't asleep, for example.Respiratory rate could maybe be gotten by accelerometer, but could also be inferred from heartrate and body data entered when you set it up, hard to say for sure, but they have a few sensors and boatloads of data to draw conclusions from, so I'm sure they've devised ways to get it right most of the time.

author: metrologist
author_rank: Super Contributor
timestamp: March 13, 2019, 09:36:28 pm
content: It doesn't look like heart rate plays a huge role as the plot is very erratic from a low of 50 up to almost 85. The heart rate variance plot can go from nearly zero up to 100 ms. It does not plot active heart rate so I do not know how that varies during the day.The ring is connected to the phone once per day to download data, then the BT connection is turned off. I also never have data turned on when the app is open and I have set Android to restrict power use when the app is closed. By doing that, my data usage went from ~600MB per month back to ~200MB.

author: DaJMasta
author_rank: Super Contributor
timestamp: March 13, 2019, 09:56:41 pm
content: Actually, if I remember right, it may be able to get rough respiration from the heart rate sensor. I believe the optical sensor shines a red LED at your skin and looks for the variation in color you get with each cycle, so you may be able to see some difference in general blood oxidation and infer respiration/exertion partially from that.The accelerometer is also definitely a possibility - even if they use one that's not super sensitive (though there are definitely ones available), since breathing and such is a pretty regular activity, you could look for very small variations and have a good degree of detection accuracy by correlating those movements over a long time looking for a regular period. Even if the SNR is pretty bad at the amount of fluctuation you're looking at, if you know that the breathing rate is between say, 1Hz and 50mHz, and you only need to be able to get a usable average every minute or so, it may not be too hard to have a good idea what your breathing rate is all the time - and breathing rate usually changes noticeably when you sleep.The biology of it and the actual sensor technology is a not something I have significant experience with, but the signal processing and analysis to pick out little things is pretty fascinating, and their pool of testing data to pull little inferences out of is massive, I'm sure.