On June 7, 1870, Thomas Hall patented the electromagnetic signal apparatus for railroads–better known as the automatic electric block. This handy device prevented trains from colliding. Hall, who was from Stamford, improved the signaling system in 1867 when installing several of them on the New York & Harlem Railroad. However, Hall didn’t receive his patent, No. 103,875, until 1870.
The device featured a lever that, when struck by the wheels of a locomotive, would complete a connection that sent an electric current to turn on the “danger” signal until the train had moved out of the block. Hall’s Electric Railway-Switch and Draw-Bridge Signal Company was located in New Haven, Connecticut.