An eMarker device is used in a cable electrically connected between a first port and a second port, wherein the cable includes a configuration channel communication wire. The eMarker device comprises: a first eMarker disposed near the first port and including a first active protection module coupled to the configuration channel communication wire, wherein the first eMarker is electrically connected to a first power pin of the first port and a second power pin of the second port; and a second eMarker disposed near the second port and including a second active protection module coupled to the configuration channel communication wire, wherein either of the first active protection module and the second active protection module changes an electric characteristic of the configuration channel communication wire to have the first port detect a disconnecting status of the second port when a specified event happens.