SVAT VISS6002 Handsfree 2-Wire Video Intercom System (Black & White) Two-wire system design allows you to use your existing doorbell wires to install. Full two way communication and door strike compatible 6 Infrared LEDs lets you see in the dark 4 inch flat CRT screen Max Wiring distance: 90ft using 0.5mm cable, 160ft using 0.65mm cable