How the Morse Telegraph works The key is pressed to start communication and allow current to flow into the coil of the receiving machine. The iron rod within the coil is magnetized, and attracts the iron leaf. The key is released, shutting off the current, and the spring forces the iron leaf away from the iron bar. This movement of the iron leaf leaves a record on paper tape. At first a needle was pressed into the paper to emboss the record, but later versions used a pen or a tone (acoustic device) for recording. Diagram