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With either 6", 10" or 4" adaptabels.
I think it could be a voice communication panel. I remember my mom telling me that when the alarm goes off for fire drills, Her boss comes on the intercom, telling them where the fire is, for pratice.
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They have bells with a voice evac system? If they have voice evac system why don’t they have just the speakers for the alarms? I wonder if the bells stop when the voice comes on, or elese noone will hear the voice instructions.