The Wii’s sensor bar is a completely mis-named, because it DOES NOT sensor anything. It is actually the emitter rather than receiver. It just emits IR lights, so the camera inside the Wiimote can track these lights and figure out where it is in space. The position information is then transmitted to the wii-console via bluetooth. The following video on youtube probably deserves credit for this discovery.

[youtube JTGSkYRDpWY sensorbar explained]