... 4ghz,mic built in 5.wireless microphone Wireless Microphone for Teachers,USB Wireless Microphone,Bluetooth Wireless MicrophoneFor handsfree convenience, ... and processor are combined in this all-in-one unit, for revolutionary, cable-free convenience. Feature:1.Portable,convinient,microphone ... Lithium Battery Environmental protection.9. It can work for 30 hours,standby time :60 days.More specifications: