Wikipedia
TrackIR is an optical motion tracking game controller for Microsoft Windows, created by NaturalPoint Inc. that tracks head motions with up to six degrees of freedom ( 6DOF) in later models, allowing handsfree view control for improved game immersiveness and situational awareness. Head position and orientation are measured by a purpose-built video camera, mounted on top of the user's monitor, which observes invisible infrared (IR) light (hence the name) reflected or emitted by markers on a rigid model worn by the user. TrackIR software is used to access and control the camera, as well as adjust tracking and manage game profiles. The ratio of actual head movement to virtual head movement can be changed, allowing the virtual head to turn 180 degrees whilst the user still looks at the monitor.
TrackIR has promoted and established head tracking in PC games, achieving support from many developers, particularly those involved in the simulation genre. In the process its interface has become the de facto standard for head-tracking game view control, although other commercial and non-commercial solutions exist.
NaturalPoint have maintained the possibility of TrackIR eventually entering the video game console market.