A relay is an electrically operated switch that consist of a set of input terminals for one or more signals, and output contact points. A different type of physical state can be obtained by operating the contacts at any time to change connectivity between its control inputs and outputs. Relays are the perfect solution for those who need to control a circuit by an independent low-power signal or when several circuits must be controlled with one single switch. Relays were first used in long distance telegraphs as repeaters, refreshing and transmitting signals coming into from one switchboard onto another board much farther away. This was how they got their name–relay meaning “to pass on.” They became widely popular during phone exchanges because of switches that made logical operations easy so telephones could communicate clearly over hundreds of miles without interference.