fire alarm
noun [ C ] uk/ˈfaɪər əˌlɑːm/ us/ˈfaɪr əˌlɑːrm/
火警报警器，火警钟;火警报警器开关
a device such as a bell or siren that warns the people in a building that the building is on fire
If the fire alarm goes off (= starts making a sound), leave the building calmly. 如果火警报警器响了，请保持镇定，离开大楼。