I have both an Apple Watch 8 and the Garmin Fenix and I use the Fenix for sleep tracking. I find the Apple Watch to be too general with the stats. The Fenix gives a lot more detail. You can debate if the extra detail is useful or not. I also like the heart rate variability tracking with the Fenix (it seems to mirror how tire I feel pretty well). Lastly, the Fenix can hold a charge for several days. I can use it to sleep track and run and repeat and it charges quickly. If I sleep track with my Apple Watch, it may not have enough battery for the rest of the day. I run with both -- the Fenix for running specific tracking and the Apple for calling friends, listening to Audible, or podcasts.
That would be an understatement, are you running/cycling a lot outside, or is it a smaller model (thus small battery because physics)?
Mine (Fenix 7) holds charge for 15 days minimum and that's with tracking workouts 3-5x/week (no GPS though, winter so I treadmill for runs). On a couple of months where I didn't do sports it held up 25-30 days.
I have SpO2 tracking disabled because it's quite battery intensive and the only use for it would be high altitude acclimation, although I must admit I looked at it during my "stop smoking" process.
my experience with garmin (vivoactive, not fenix) was that they had all kinds of precision and detail, but it also didn't even notice when i got up to pee in the middle of the night - just a straight line through the graphs as though i hadn't woken up at all. that was the end of my trust in their sleep tracking.
Mine reliably notices that I woke up and immediately go under when my wife comes home late in the night, which happens basically every day (because bartender) so I get somewhat statistically significant results in that regard.
The Quantified Scientist does very detailed, measurement-based tests on all sort of smart watches, you might want to see where your device stands in his charts in terms of accuracy.
my garmin was really good at picking up my heart rate. there was one time i had it in a waist pack, and i was wearing a chest strap that was not paired to the garmin, and the garmin managed to pick up a pretty accurate heart rate for most of a bike ride.
I recently got a Fenix 7, but not for sleep tracking purposes. I find it ok. I definitely think it isn't great at measuring wakefulness at night, but I also have a very low HR and high HRV (while awake), which so this causes the margin for error in the device to be very low.
As I usually say, all of the devices are good enough. You're getting historical data about what your body did. You can't go back and change it anyway. I don't see real value in knowing my historical sleep data.
Not OP but I have a Fenix 7x. What happens very infrequently is that I would wake up during the night, and then be absolutely still (I'm trying to go back to sleep) except for checking my watch every 15-20mn. This does not get detected as "awake" the following morning.
I don't really care because I got this watch so I can upload a track and follow it while recording various metrics during 5+ days, and for this it works perfectly.
There are two data points you need to accurately track sleep: Motion and respiration rate. With that information you can identify light sleep vs. deep sleep, and sometimes you can differentiate between light sleep and being still.
Source: Worked on the ResMed S+ and got a theory dump from the PhDs running the project.
Sleep versus awake from a sensor on the wrist is always going to be subject to wide error bars.
Source: worked on an experiment trying to make people fall asleep while driving (in a simulated environment so it was safe- I built the simulated environment). It took a lot of EEG wires and gel in subject's hair etc. to accurately figure that out.
Same experience for me. If I wake up but lie still it's not nearly as accurate. What I do find useful is the Body Battery score, that generally maps well to how I feel the next day. And the Stress Score is an eerily good indicator of when I'm getting sick and when the illness is stopping.
Data aside, neither are ideal. I can’t sleep with the Apple Watch because it needs to be charged while I sleep to get through the day, and the Fenix is too heavy for my wrist at night. I use an old Mi Band, which tracks approximate data that suits me.
According to reviewers, Mi Bands and generally all of Xiaomi's devices are fairly bad at sleep tracking. So much so that it's almost pointless to use them for that.
I know it’s fully anecdotal, but my Xiaomi/Huami (former Xiaomi sub-brand) devices have matched up sleep duration quite well with what I feel in the morning - and I’m quite sensitive to less sleep. I think it’s quite good for sleep duration, but I don’t rely on REM duration etc as I don’t have much use for it. When it predicts a good sleep score I’ve definitely slept well, though sometimes it gives a lesser score even when I don’t appear to have slept poorly.
(I’ve used a Mi Band 1, an Amazfit Bip, and currently an Amazfit Band 7.)
FWIW, I charge my watch while taking a shower before bed and in the morning, and that seems to be enough to get me through the day and through the night.
