The VRU (Voice Recognition Unit) had only two compatible games: Hey You, Pikachu! and Densha de Go! 64. A VRU was included with every copy of Hey You, Pikachu! and was required to play the game. Densha de Go! 64 did not require the VRU, and as such, it was sold separately. It consisted of a ballast that was connected to controller port 4 of the system, a microphone, a yellow foam cover for the microphone, and a clip for clipping the microphone to the controller. The VRU was calibrated for best recognition of a high-pitched voice, such as a child's voice. As a result, adults and teenagers are less likely to have their speech recognized properly by the VRU. VRUs are region dependant, and a USA region VRU cannot be used with Japanese games and vice versa (foreign region VRUs are not detected by the games). No VRU compatible game was launched on the EUR region (PAL, Europe), so there's no EUR region VRU. A similar device was also released for the Wii called the Wii Speak.