The definition of simultaneous interpretation equipment is somewhat debatable and yet the first time the equipment was used as it is being known today is believed to be after the conclusion if the Second World War in 1945 at the trials of Nuremberg.
However, before it, it was way back in the 1920s when Edward Filene, a businessman in the United States of America was known to propose it. Filene is believed to have supported the League of Nations and shared his idea of the use of audio equipment to the League so that the interpreters could use the headsets to offer the audio form of their translations to the listeners. However, this idea of his could not be strictly termed as being a part of simultaneous interpretation. Rather, his proposal was more in the lines of first getting the speech translated and subsequently reading out the translation by the interpreter while the original speaker gave the speech on a stage. Before that the organization used consecutive interpretation. Many others like Filene found the interpretation methodology quite inefficient and slow.
There are two major functions offered by the interpretation equipment of today. Firstly, they help in distributing the audio of the speaker to the interpreters. Secondly, they distribute the interpretation of the interpreter to the listeners who require it rather than distributing to others who do not require it.