Thanks for mentioning the Zeo. I used it for a month a few years ago. It was ahead of its time using 1-wire EEG monitoring. I felt the REM graph was actually telling me something. Any sleep monitor to try and take its place must be EEG based. An accelerometer is inadequate for sleep monitoring.

The closest thing I know of is the OpenBCI.com project (Brain-Computer Interface) which is entirely an EEG project.

I loved the idea of the Zeo, but as comfortable as the headband was, I never did manage to fall asleep with it on. I guess I am just super sensitive to things on my head while in bed. I ended up using the Zeo as a toy to do interesting BCI hacks with.

You don't have to wear a chest strap on your forehead.

It's inferior to the Zeo, but is not out of business, unlike Zeo. :(

Zeo is dead