A device used for measuring the orientation of a human head about one or two axes and converting that information into an electrical signal in the analog or digital domain includes a headset and includes one or two electromechanical orientation sensors which provide an electrical signal that corresponds...http://www.google.com/patents/US5323174?utm_source=gb-gplus-sharePatent US5323174 - Device for determining an orientation of at least a portion of a living body
