The status display complies with the "two senses" principle. It provides both an optical and an acoustic signal of which function is currently active. This affords the deaf and hard of hearing clear visual feedback from the intercom.
The doorbell has been rung: The status display confirms the door call by means of an optical signal.
The mouth symbol signals: It is now possible to speak.
The door release is actuated: The door can be opened.
The fourth symbol signals: Currently unable to establish a connection.