The Audion made pratical radio braodcasts a reality. Prior to its introduction radios had typically used semiconductor rectifiers known as "cat's hairs" which were unreliable and offered no amplification. Such systems required the user to listen to the signal though tiny headphones with almost no volume. The Audion allowed the signal to be amplified to any desired level, typically by placing the output of one Audion into the grid of the next, eventually providing more than enough current to drive a full-sized speaker. By the 1920s such "tube radios" were a fixture of most western households, and remained so until the introduction of the transistor in the 1950s.
De Forest was granted a patent for the Audion on November 13, 1906. He continued to claim that he developed the Audion independently from Ambrose Fleming's earlier research, and became a fixture at many radio-related patent disputes. De Forest was famous for saying that he "didn't know why it worked, it just did". In 1914 Edwin Armstrong published an explaination of the Audion, and when the two later faced each other in a dispute over FM, Armstong was able to conclusively demonstrate De Forest still had no idea how it worked.