Devices that detect when someone is falling asleep I'm wondering what types of devices exist that can detect how close someone is to falling asleep. I have heard of several devices that may be able to do this, but I haven't been able to find very solid information.


EEG: I assume these could detect falling asleep quite effectively; though, I'd like to know if there are any other devices that would work as well.
EKG/ECG: I found this paper that claims you can use a Lorenz plot to detect correlation between heartrate and falling asleep.
GSR: A lot of people say a GSR can be used, but I have yet to find any papers/data that describe the correlation between GSR and falling asleep
Pulse Oximeter: someone mentioned to me that these work as well, though I haven't been able to find much information
I've used the Zeo (http://www.myzeo.com/sleep/). It seems to work pretty well. It tracks which stage of sleep you are using a very basic EEG. There are some details on how it operates here: http://radar.oreilly.com/2009/10/how-the-zeo-sleep-device-works.html

As I said, I've used it in the past and from what I can tell, it seems to be pretty accurate, assuming you don't knock the sensor off while you're sleeping.