An embodiment of the present disclosure provides an intercom system including a cloud server, and a relay gateway. The cloud server is configured to receive a trigger signal from a visitor door station, and to send a notification when the cloud server receives the trigger signal from the visitor door station. In one embodiment, the relay gateway is configured to receive the notification from the cloud server and to send the notification to one of a plurality of local intercom stations via one of plurality of hard wires, the hard wires being connected to the local intercom stations, respectively. In one embodiment, the cloud server is configured to send the notification to a remote intercom device that corresponds to the one of the plurality of the local intercom stations.