The only downside to the Apple Watch in my book is the short battery life which should theoretically make it impractical for sleep tracking.
I was recently stupefied to discover Nokia Steel  and how virtually unknown it is to the general public, my former self included. It comes with great design, no bullshit digital screen, the usual tracking features, and most importantly seems like it's a return to form for Nokia, considering their country's outstanding design heritage.
edit: lol I forgot to mention the best part. THE BATTERY LASTS EIGHT MONTHS
I'm skeptical about the accuracy of applications like this running on Apple Watch. I bought the Apple Watch Series 3 precisely because of articles like this. I now routinely get messages about how I've achieved my standing goal - while lying in bed watching TV or working on my laptop. If it can't accurately tell whether you're lying down or standing, it is unimaginable to me that it could be remotely accurate in detecting far more complex conditions.
Danger, danger: heavily regulated waters ahead! Remember these words well: "This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease."
I'm one of the co-founders of Cardiogram and involved in this study -- happy to answer questions if folks have them!
(EDIT: heading to bed, but will answer questions in the morning!)
As someone with diagnosed apnea I have so many doubts about this.
Machines to diagnose apnea have lots of sensors including electrodes, "chest-band" pulsometers, and "saturationmeters". I have asked doctors about capabilities of smart devices for apnea control or detection, all I got was laughs.
Sorry but I think this is not true. Go and see your doctor.
I went to sleep wearing my Apple Watch one night and awoke to a few hundred irregular heartbeat notifications.
They weren’t legit. The watch just can’t get a good heart rate reading if it’s not situated perfectly on your wrist, and while sleeping it was pushed one way or another often enough to be useless.
Interesting, but are people really sleeping with their Apple Watch on? I don't you need to charge it every night?
Does anyone know how we can use this today?
It's quite interesting - the way we have evolved as a society has completely broken the link between "us and our body". We have stopped listening to it a long time ago. If we really listened to our bodies, we wouldn't eat/drink/consume stuff we don't need, we wouldn't be overweight, and we'd rapidly be aware of any health-related imbalance which needs restoring.
But no, we forget our original (and free-of-charge) way of functioning and desperately turn to commercial and unnatural solutions.
As a start, I recommend looking into the mindful meditation technique, championed by pioneers like John Kabat-Zinn.
97% accuracy seems high, but with an approximate sales number of 10 million Apple watches, it will give 300 thousand users an incorrect diagnosis.
I love my Apple Watch series 1.
The one thing that’s frustrating is installing any apps on it takes a really long time.
In the Future Everyone will Wear a Smartwatch
Unless you have a heart murmur like I do.
Then: it just lies.
I think this is a great feature provided Apple won't collect the data.
 Btw, I really don't mind getting down voted, but would appreciate to see your opinion on why you think Apple collecting that data is a good idea.