A sports watch by itself will not improve our sleep – it will always be some of our actions. However, new watches that track elements of sleep can provide a great deal of useful feedback.
So far, my experience with it is only partially satisfactory. Garmin has a very sophisticated way of tracking sleep that includes stress (measured by skin resistance), skin temperature, sleep length, number of “restless” moments, light sleep, deep sleep, and REM. I’m not sure how it measures all that, but I think it’s only partially accurate in that sense (hence the partial satisfaction with the correlation between what the watch says and how I subjectively assess the quality of sleep).
For example, sometimes I have a lot of dreams and the REM phase should be long, but the watch says it is not. Or, sometimes during the day, the watch “catches” me to doze (nap), and there is no way that I was asleep because, for example, yesterday, I was driving the car at those moments. :-)
The technology is not yet so precise that it would be 100% accurate, but it still seems to me that it is useful. For example, I noticed a high correlation between the measured stress during sleep (Garmin measures it in numbers from 1 to 100) and the feeling in the morning. Of course, the lower the stress, the better. In this sense, it is interesting how much digestion raises stress during sleep. Take a light dinner around 18:30, and stress during the night will be low (in my case, 15-20). A slightly larger dinner just half an hour later and the stress could be twice as high. Maybe not everyone reacts like that, but in this sense, I think that the feedback from the watch is a special thing: you can see for yourself, through adjustments to your daily routine, how certain actions affect the objective measures provided by the watch.
Of the other measures that are well hit, it seems to me to be SpO2 or Puls Ox, which is the blood oxygen saturation level. Admittedly, you will need it if you often change the altitude you are at, but it has an impact on the quality of rest after sleeping.
One more thing that is the most useful in my experience is HRV (heart rate variability). The heart beats with a certain rhythm but has small variations (so it does not work like a machine, but “dances” a little). HRV is measured in milliseconds and can range from approximately 10 to 100 milliseconds. The older you are biologically, or the more exhausted you are, the lower the HRV. The younger or more rested you are biologically, the higher the HRV. The point is that you cannot measure HRV in short intervals, but it is best to do it during sleep.
The average HRV during sleep is excellent information not only about the quality of sleep but also about the readiness of your body to bear additional efforts. Through HRV, for example, you can adjust the type of training during the week. When it is higher, feel free to strain your body; when it is lower, do recovery training. You can also use the movement of HRV during the night to check the procedures and daily routine, as well as how much and how they affect the quality of sleep.
The overall rating of wearing the sports watch during sleep, according to my experience, is: positive and useful. If you take the data with a “grain of salt” (meaning not literally but with the awareness that the watch is not a perfect medical instrument, but an instrument that is “good enough” for amateur and recreational purposes) they can help you test what influence a certain type of activity has on sleep, and even more for choosing and dosing the type and intensity of exercise during the day.