For a brief time there was a consumer product "Zeo sleep monitor" which was a legitimate EEG-style brainwave headband you would wear to sleep. From what I recall, comparing it's results to those of in-lab sleep studies, it was fairly accurate.
Sadly they went out of business as it was a fairly niche product and pretty expensive.
I fear they may follow the same course as Zeo at those prices though. For typical consumers I would imagine only the most fervent "quantified self" types are going to be comfortable spending $500 for sleep tracking.
I'm interested though :)
However, their Android app is still on Google Play, and you can find used models on eBay. There's also a cottage industry making replacement headbands (which wear out).
At least there was 3-4 years ago when I last used mine. I haven't tried it since.