Signedplate on top panel: WESTERN ELECTRIC
plate on top panel: LE MATERIÉL TÉLÉPHONIQUE / SOCIÉTÉ ANONYME / Ancienne Maison G. ABOILARD & Cie / 46, AVENUE DE BRETEUIL - PARIS
FunctionThe buzzerphone is a wire telegraph developed during World War I designed to avoid message interception by the enemy.
The wire transmitter / receiver (one side of the line may use ground) uses very low direct current, about 60 microamps, avoiding interception by either induction (for being DC) or current leakage (for using very small current).
At the receiving unit, a "howler", an actual telephone receiver and transmitter, modulates the signal so it can be heard in the receiving operator's earpiece. The howler in the sending operator's unit provides feedback (sidetone) to him.
The buzzerphone could also be used as a telephone, albeit less securely.
A good description of the advantages of this instrument is found in the Report of the Chief Signal Officer (to the U.S. Secretary of War), 1919, available on Google Books here.
ProvenanceAccording to a tag, it was used at the Cruft Laboratory, Harvard University.