Samuel F.B. Morse invented the code, which bears his name, that is transmitted via telegraph (and radio). The initial invention provided for dots and dashes to be printed on a moving piece of paper. Combinations of dots and dashes represented letters and numbers. Morse's telegraph receiver was widely adopted.

The paper-recording message receiver was not as well received, principally because the sound of the clicking armature could be "read" in the same manner as the paper. Signaling distances were improved by the use of a relay, an electromagnet receiver that uses the power from the line to operate a switch providing battery power to key a further length of telegraph line. Relays were the only form of amplifier in use until the invention of the triode tube by Lee De Forest in 1907.