The droid caller, also referred to as a caller, control box, control device or owner, was a handheld transmitter device that was used to summon a droid or activate its restraining bolt.
Callers were designed with three basic commands: "COME" called a droid forward, "STOP" forced it to halt, and "ORDERS" caused it to enact any commands, within the droid's operating parameters, given verbally.
The Jawas of Tatooine often used callers to control their droids before selling them. As a seven-year-old child, Luke Skywalker created a makeshift droid caller in order to stargaze without his aunt and uncle's droids detecting him. It was confiscated when Owen Lars discovered him. Both Luke Skywalker and Han Solo carried callers around 0 BBY. Luke used his caller to bring C-3PO out of hiding after R2-D2 departed to find Obi-Wan Kenobi.
Jaybo Hood on Iego possessed a reprogrammed droid caller which he could use to control battle droids.