TrackIR is a headtracking device that currently is quite popular amongst gamers, especially in the simulation community.
It consists of a small device to be placed on top of the monitor and a prepared base cap with three IR reflecting strips.
JTrackIR is my Java binding. Not a big thing, but maybe useful to somebody.

TrackIR shows an impressive resolution and supports all 6 axes (x,y,z,yaw,pitch,roll). So it not only detects the heads attitude but also the translational position and even the heads distance from the screen.

The device is not cheap but also not extraordinary expensive and definitely worth the money if you have a good use-case.

As with all parts of the Distributed RealTime Simulation project on SourceForge, the source is available from cvs.
The Java source code is free while I'm not allowed to opensource the C/C++ code accessing the TrackIR DLL because it is covered under an NDA. So you have to refer to the compiled binary located in the bin directory.

The API is stupid simple. For there can only be a single device, the API layout is completely static. Here are parts of it:

public static void setDeveloperID( int id );
public static void update();
public static boolean isOperational();
public static float getRoll();
public static float getPitch();
public static float getYaw();
public static float getX();
public static float getY();
public static float getZ();
...

The jar file in the bin folder there also contains a simple test UI that paints the values as it is delivered by the device.

request an SDK-->.

Currently, JTrackIR is not yet embodied to FlyingGuns. My own architecture placed the camera far away from the input system, so they are hard to connect :). But there is still some hope.

If you think controlling something with your head and you like to use your head not only for its mental power, JTrackIR allows you to do that easily and your application might proudly show a new logo: