My generic Chinese fitness watch measures my heart rate and sleep patterns 24/7. It has an associated app which displays very high level summary information on my phone via an associated app.
The watch does however send all the data it has collected in a very non-standard file format every day via Bluetooth to my phone where it is stored deep in the Android file system. With some considerable processing, these files can be freed of the useful information they hide.
For example, the chart above (click to enlarge) shows my sleep patterns from 16th October 2020 until 10th February 2021. Red indicates deep sleep, pink is light sleep, and white is time spent awake.
The first six hours of sleep are delineated with vertical lines. Everything to the right of that is bonus sleep. Apparently I fall asleep almost instantly every night, have light sleep for 20 minutes or so, and then enter my first and longest period of deep sleep.
From the chart above, after the first few hours of sleep, the percentage of deep sleep reduces as it is replaced by light sleep. After six hours of sleep, on average I have had over two hours of deep sleep, and very little time awake (none of which I remember).
The above pivot table results from Excel show that Saturday is my official sleep-in day. Sunday, I like to go for a long run as soon as I wake up, and the rest of the week’s sleep is dictated to by the kids’ school and work etc.