The inventor of the first exchange for telephone service. Holmes's father had invented and installed the centralized burglar alarm system in 1858 in Boston, Massachusetts. In 1877, Holmes obtained telephone numbers 6 and 7, and attached them to a wire in his office. He then placed six box telephones on a new shelf in his office. During the daylight hours, the telephone exchange operator could switch any of these telephones into connection with the burglar alarm wires and any two of the six wires could be joined by a wire cord. At night, when the telephone operator was off duty, the telephone network reverted to a burglar alarm network. See also central office.