... waterproof 3.network function IP video door phone, DVR video door phone,Video door phone, 4CH video door phone. 2-way audio ... Linux operating system,Multi-language interfaces*Quad-or-full screen display, good video, quality and high resolution*Demountable, network access, Remote ... 4-channel CCTV video inputs, 2-channel video door phone inputs)*4 channel monitor or single on screen display.*2-way audio ...