mm my virtual i\o from i-glasses has a tracker in the back part of the HMD.
it has a three degree of freedom orientation tracker.
here is a link of the picture of the hmd that i have.
http://graphics.stanford.edu/infrast.../iglasses.html
http://www.xolmatic.com/xprojects/i-glasses.htm
i know that the tracker works because i tried with other software that we have in our lab