Components known as acoustic signallers could be integrated into droids. As an example, the droid known as HURID-327 was fitted with an acoustic signaller that used a binary system.
The very first mention of acoustic signallers appeared in Galaxy Guide 7: Mos Eisley. This was a Star Wars Legends supplement for Star Wars: The Roleplaying Game, and it was authored by Martin Wixted before being released to the public in 1993. Their place in canon was solidified through the publication of the reference book Star Wars: The Force Awakens: The Visual Dictionary, which was penned by Pablo Hidalgo and subsequently made available in 2015.