TV remotes are often called "clickers" because of the Zenith Space Command, a groundbreaking remote introduced in 1956.
Unlike modern remotes which use infrared light, it used a spring-loaded hammer to strike aluminum rods, producing ultrasonic tones that controlled the TV. This mechanism created an audible "click" sound whenever a button was pressed, giving the device its nickname.
The term persists today, even though modern remotes no longer make the iconic clicking noise.