vistor calling, video intercom,lock release, monitoring 4-wires connection,Night vistion,Backlight Product Description1.With good video intercom2.Ultra thin 2 ... .3cm, 4 inch handfree3.vistor calling, video intercom4.lock release, monitoring5.Four wires system, easy to ... .Max support 2 bells with 4 monitors 9.Intercom between monitors 10.ID card reader optional outdoor bell 4" villa door entry