VOCOPRO SilentSymphony-Duo Professional Headphones Transmitter and Receiver Headset sold separately Operates in the 900MHz, clear of TV Station Interference Broadcast Audio to an Unlimited Number of Wireless Headphone Sets Use up to 3 Transmitters Simultaneously Internal Battery Built Into Transmitter for Remote Use Transmission Power Level Toggle (High/Low) Available Stereo RCA Audio Input on transmitter Available Stereo 1/8 Audio Output on Each Wireless Headphone Set Headphones have an 18Hr Battery Life Off Two AAA Batteries