The black MXW6 Cardioid Boundary Transmitter from Shure is a bidirectional boundary transmitter with a built-in cardioid microphone, designed for use with Shure's Microflex wireless conference system. The unit has an earphone output that allows you to monitor return audio, useful for translations or programming material. It has a concealed power switch to prevent you from accidentally turning off the unit. It transmits your audio with AES 256-bit encryption for secure broadcasting. The MXW6's built-in rechargeable battery can provide up to 9 hours of operation.