A basic annunciator in lC19 consists of a bell fixed to an often ornate wooden box that stores the receiver’s mechanization and frames its visual interface. The face is divided into discrete units, each comprised of a linguistic or numeral signifier representing the location of a calling device and an armature capable of rest in two positions. When a call button is depressed, two types of data are transmitted simultaneously by the annunciator through two binary codes, one visual and one aural. Dormancy and silence indicate that no external message is being conveyed to the central hub. A call closes the electrical circuit; the struck or vibrating bell audibly announces a change in the visible interface, which has shifted an individual annunciator’s lever from one position to a second.