These grew in popularity in the late 19th and early 20th centuries until the rise of radio in the 1930s.
Player pianos could be played in the same way as a conventional piano, but they also contained a roll inside which could read perforated paper. The information contained on the paper not only mechanically operated the notes of the music but could also contain other information such as dynamics, tone, tempo and expression.
Listen as this player piano performs a famous ragtime piece.
Watch how the perforations made in the paper activate the keys.