a fire alarm system is installed in a building containing therein a large number of rooms such as inns , hotels , office buildings and the like . the system comprises fire detectors , microphones and speakers installed in different rooms and connected to an administration room , so that when one of the fire detectors is put into operation , the microphone and the speaker turn on and inform the administration room of the operation of the fire detector . a conversation can be exchanged between the administration room and the room in which the fire detector is put into operation .