Functions & features: - The resolution & stability of this item is better then the congener products in mainland China. - Solid metal case. - High resolution of over 550 TV lines in center. - Easy hook up with up to 4 cameras via 6-PIN connecting cable,(standard 20M cable) - Micro processor controlled four channel sequential switching. - Built in alarm function. Any alarm sensor can be connected via DC-301 camera. - Two way audio allows communication between monitor and camera.