DVR is widely used in the security monitoring system because it has excellent performance compared with VCR. In this paper, the new DVR interfaces and repeaters enhancing the performance of the existing DVR have been designed and implemented, which enables a large-scaled security monitoring system to be built economically. A repeater in this paper connects 8 monitoring terminals to 2 channels of DVR and a DVR interface manages 16 repeaters to be able to accommodate 128 monitoring terminals. Eventually, the implemented system has a quadruple scalability compared to the existing systems and can reduce the installation cost substantially by using cost-effective UTP cables instead of coaxial cables. And the system could be effectively used in various environments and conditions because various functions such as video transmission, audio communication, emergency call, and RFID card are integrated into the system.