an indicator that announces which electrical circuit has been active (as on a telephone switchboard)
annunciator详细解释
an.nun.ci.a.tor n.（名词）One that announces, especially an electrical signaling device used in hotels or offices to indicate the sources of calls on a switchboard.信号器，示号器：宣告物，尤指饭店或办公室中使用的一种电子信号装置，用来指示交换台上的呼叫信号来源
