What I think that technically needs to happen at minimum is:
3. EEG (brainwaves)
That will be the minimum viable product that may become as good as polysomnography and bring sleep lab tech to your home. Dreem claims to be doing this, but it isn't clear whether their claims are true.
Companies like Zeo produced presumably good results, yet they are now bankrupt. It's quite infuriating to see. So there's a business model (or simply an organizational problem at Zeo at the time) and I'm not clear what it is. The tech is already here! For example, Somté PSG shows that it can be done, and I'm simply thinking to myself: this could be more user friendly, couldn't it? 
Marketing-wise, I think the following needs to happen:
1. Get multiple unrelated universities to test your device against polysomnography and iterate against it.
2. Once it's within the 90% agreement range, then even make a YouTube video about such tests. Keep testing it against the golden standard, because if you are as good as the golden standard, then you can really state you track sleep.
3. Also test different PSGs with each other, because while PSG is the golden standard, no study told to what extent they actually agree on sleep metrics. There probably are studies on it but they didn't test this (or comment on it even, I believe) when wearables such as a Fitbit were studied as well.
4. Make ridiculous cool claims like everyone is already doing. Really go for the full appeal to authority, like Dreem is doing (nothing new).
I can't imagine having a headset and sleeping as I normally sleep. The results wouldn't be fully representative.
I've noticed I don't have issues wearing something around my wrist, but I get that that's a factor. I'm also noticing that I don't get anxious about the data, because it's all a bit guesswork anyway, so I guess I'd want to see an aggregate form of data if it gets more precise, so that it still feels a bit like guesswork, unless there's something wrong in a big way.
Also, as appealing as the device sounds, I'm terrified of giving this kind of personal data away to a tech company:
>Dreem works as a long-term sleep expert and one-on-one coach: it monitors your sleep habits and sleep quality for a week, asks you for a lot of more details about your life (day and night), and downloads your activity data from other personal health apps
The overly suave marketing on the dreem site makes me wary as well. Between personal data abuses and shady marketing practices, how is anyone supposed to trust modern tech anymore?
I want to know whether one can get their nightly EEG data.
Type (sleep, nap, relax)
Sleep Onset Duration
Light Sleep Duration
Deep Sleep Duration
Wake After Sleep Onset
Number of awakenings
Mean Heart Rate
Mean Respiration CPM
Number of Stimulations
There appear to be two terminals on the band which are not used by the normal user. I assume they are for flashing the firmware on bricked devices.
"Unfortunately, we do not provide you with a raw data report containing your EEG data. However, we do provide it via user-friendly hypnogram via the Dreem app."
I just looked into this 2 days ago! While I'm not the OP, this submission happens to be one of the most exciting articles I found (I should've submitted it :P). I was asking myself whether I should update my Fitbit Flex 2 to a Fitbit Versa or an Apple Watch or anything else really.
The answer is: don't upgrade, keep the Fitbit Flex 2, it's about as good as journalling your own sleep times and that's all I need really, a very rough estimate. More importantly, the newer wearable devices are not good enough at giving a reliable breakdown of your sleep that polysomnography (the gold standard would give).
With that said: the Basic Health Tracker (doesn't exist anymore, I think), Oura Ring, Philips Actiwatch Spectrum were all able to do things that trackers that the Fitbit and other wearables couldn't.
> Only mean values of sleep efficiency (time asleep/time in bed) from Actiwatch correlated with PSG, yet this correlation was weak. 
> Light sleep time differed from PSG (nREM1 + nREM2) for all devices. Measures of Deep sleep time did not differ from PSG (SWS + REM) for Basis. 
> From EBE analysis, ŌURA ring had a 96% sensitivity to detect sleep, and agreement of 65%, 51%, and 61%, in detecting "light sleep" (N1), "deep sleep" (N2 + N3), and REM sleep, respectively. 
A good literature review on it is .
Some facts (which can be found in  or its cited papers):
* All trackers overestimate sleep by about 30 minutes.
* The biggest problem for all these wearable trackers are: estimating when you're simply lying awake in bed but you're not moving (it thinks you're asleep).
* Devices like the Fitbit Flex are about as accurate as sleep journalling with regards to total sleep time.
Dreem has the following issues. It's hard to see whether their scientific papers are peer-reviewed. Yes, they produce science articles in PDF formats but not in journals. Yes, they collaborate with universities but it isn't clear how. Nothing is peer reviewed and almost nothing seems to be cited. This was echoed in a Gizmodo article , but I figured it out myself first.
I'm not saying they aren't legit, because another thing I have noticed is that the scientific community is a bit but not too keen on testing these devices with the golden standard (polysomnography/PSG). There is still space for a startup who is clearly capable of demonstrating this and other research institutes confirming it independently for their device.
Edit: I hope I gave enough sources to make my comment a bit credible.
 obtained from abstract @ https://www.ncbi.nlm.nih.gov/pubmed/27164110
 obtained from abstract @ https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8648428