Forget about the Wii controller, ever wonder how the NES Zapper worked? Wikipedia writes: “When the [Zapper] trigger was pulled, the game blanked out the screen with a black background for one frame, then, for one additional frame, drew a solid white rectangle around the sprite the user was supposed to be shooting at… Zapper would detect these changes in intensity and send a signal to the NES to indicate whether it was over a lit pixel or not. A drop followed by a spike in intensity signaled a hit.”
Follow the link for more Zapper information than one should know.