Thought I would just add my experiences with the first couple of weeks of sleep tracking with my 245. I see lots of threads complaining about the Garmin sleep tracking accuracy and capabilities so I am getting the impression that it is not really very accurate. But just in case anyone has some suggestions as to how I might improve my sleep tracking, here are my observations and issues:
It seems the device is depending almost entirely on movement and these first few points/questions have to do with that. I guess it makes sense that movement would be the only way for Garmin to determine sleep as it is only strapped to your wrist but that lead to accuracy issues for other people too? The 245 it seems to start saying I am asleep when I am reading in bed for an hour or so before actually going to sleep. Also in the morning it always shows many, sometimes over 100, steps, even if I have not left the bed all night. I do tend to sleep on my stomach with my arms up under my pillow so the watch may move around a bit, even when I am sleeping. It does however seem to accurately show if I actually awake during the night. This I know from remembering that I woke up once or twice, and then seeing that reflected accurately on the timeline.
Another observation is that I do not ever wake unrefreshed and I usually sleep 7-9 hours. I am never tired during the day. I have never been told that I am a restless sleeper or that I snore or breathe loudly during sleep. Never been told I sleep anything other than peacefully with even breathing. However, the watch almost never shows deep sleep and when it does it is only a couple or a few minutes. The deep sleep it might report also comes several hours into the night, rather than near the beginning of the night where it should normally appear. The device shows mainly light sleep, interspersed by many (8 to 14) shorter periods of REM.
Lastly the Pulse Ox and respiration is all over the place. Pulse Ox averages in the low 90% range but at times drops briefly to low 80s. Once it single drop to 78%. Should I discount that monitoring as inaccurate?
The Pulse Ox readings may be related to respiration? Generally my sleep respiration is almost the same as my waking resting respiration, 12 to 14 breaths per minute. However during sleep the 245 registers several deep down spikes to as low as 7 breaths per minute.
How does all this compare to what others are seeing? If my arms do move a bit under my pillow or the weight of my body and head compresses my wrist and the watch, might that be why I register almost no deep sleep and so many distinct, short periods of REM?
Edit: Talked to Garmin and because I sleep with arms/wrists, under my pillow and head, the added pressure to the watch is very likely making the Pulse Ox inaccurate as that sensor is very affected by pressure of skin contact. This could also be impacting accuracy of respiration and heart rate while sleeping as the added pressure between the watch and wrist can impact the HR sensor also and that in turn affects how respiration is calculated. The Garmin rep also stated that the phases of sleep could be accurate or inaccurate depending on wrist location and how much movement when sleeping. He felt that me seeing almost no deep sleep could certainly be incorrect given that I am never tired during the day and my sleep is reported as quiet and sound. Basically if you sleep on your side or back with your wrist free and clear and do not move your arm much during sleep, it may be fairly accurate. Otherwise, probably not so much.
So the sleep tracking features seem really to be more of a curiosity and fun thing to monitor rather than anything really that accurate at all times and for all people. If I had any perceived sleep issues of my own, I would certainly not depend on one of these watches for accurate sleep information. However for ongoing heart rate, averages, maximums, etc. the watch seems very good. And I love the other tracking features, activity recording, and notifications.
