Original Item: Only One Available. This set consists of a key, battery, and buzzer. It was used for field communication over wires. It is based on the design originated in 1915 by A.C. Fuller. This design used Direct Current telegraph signals which were impossible for the enemy to intercept and decode. The design allowed much better security than the American and other 'buzzer sets' which sent code signals in the form of AC buzzing voltages. The fullerphone decodes the D.C. voltages by using an interrupter and handset or earphones.

This example is offered in good condition and appears to be complete. It comes with headset. We have not tested it and cannot verify functionality but appears to be complete.