Califone HIR-KT1 Infrared Stereo/Mono Wireless Headphone with Transmitter Operating System: Windows 2000/XP/Vista/Windows 7 32-bit & 64-bit, Mac compatible Infrared Frequency: Mono - 2.3MHz / Stereo - 2.3 & 2.8MHz Power Requirements: 2 "AAA" size alkaline batteries Automatic Sleep Mode: If no audio is played through it for 2 minutes Power on/off switch, stereo/mono switch, volume control