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Aiphone C-123LW Dual Master ChimeCom Set, Door, Masters, DAK-2S$279.33
Additional masters may be added. Each master requires a separate power supply, either the SKK-620 or 4 "C" batteries. The door station calls the masters by pressing a call button that initiates a chime.
Communication is Push to talk/release to listen at the master and hands free at the door station. Communication times out after being idle for twenty seconds.