Buzzerphone P 1917

The buzzerphone is a WWI wire telegraph designed to avoid enemy message interception and is similar to the British Fullerphone. This model was made by the French firm Le Matériel Téléphonique of Paris for the Western Electric Company.

The wire transmitter / receiver (one side of the line may use ground) uses a very low direct current, about 60 microamps to avoid interception by either induction or current leakage. 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 to the operator.

See also the later USA Buzzerphone model EE1-A.

In questo link sono elencati 176 modelli, di cui 148 con immagini e 44 con schemi.
Elenco delle radio e altri apparecchi della LMT (L.M.T.), Le Matériel Téléphonique, Radiojour; Paris, Boulogne-Billancourt