I always thought that last generation fighter combat helmets—like the Eurofighter Typhoon's Head Equipment Assembly or the F-35 demon helmet—tracked the pilot's head position using gyroscopes. It turns out that they are more Kinect than Wiimote.
Both the Typhoon HEA or the F-35 Gen II HMDS use opto-magnetic tracking technology. Cameras and sensor inside the airplane track the special three-dimensional pattern on the back of the helmet. They do it hundreds of times per second, feeding extremely accurate positioning info to the airplane's computer in real time. The computer uses this data to calculate the pilots' eye position, projecting video and targeting information inside the helmet's visor according to what he's seeing at the time.
Why they don't use simple gyroscopes and accelerometers? The obvious explanation is that the whole plane is moving at all times. Optical or opto-magnetical are the easiest, simplest way to track motion when you are doing a barrel roll at Mach 0.9. [Runway Girl, Eurofighter, VSI]