The Warning Signal (1926)

"Red" Dryden, son of a wealthy railroad magnate, who wishes to succeed independently, conceals his identity and takes a menial job on his father's line. He quickly proves himself to be extremely competent and arouses the enmity of a superintendent. The two men fight over a girl, and Red is transferred to a remote signal shack. The superintendent tampers with the warning signal at Red's shack, and the president's special thunders through, headed for a collision with another train. Red uses a radio device of his invention and alerts the engineer to the danger, preventing a disaster. Red's father learns of his son's heroism and appoints him to the presidency of the railroad.