The Wrist Communicator, commonly referred to as the wrist-com, is an item that appears in The Legend of Fox the Brave, it is mostly worn by the Storm Fighters, as well as most two-legged Pokemon on the Storming Alliance, with the exception of the Ancient Army. As its name suggests, it is used by the wearer to communicate with anyone else wearing one over long distances, and is worn on the wrist(typically the right one, regardless of the wearer's dominant hand). It was created by Cori the Charmeleon with help from Miles "Tails" Prower(Sonic Boom), and has an upgrade called the "Mega-com", which is simply the addition of a Key Stone so that people who wear a Mega Ring can have that wrist freed up.
Most everyone in the Storming Alliance uses a wrist-com. It is worn by all active Mobians on the Storm Fighters who are warriors(i.e. Austin Smith or Fang the Saber), as well as warrior Pokemon that walk on two legs(i.e. Rokky the Krokorok or Silver the Lucario), with a few exceptions(for example, Storm doesn't wear one).
Before the series: At some unknown point in time after escaping the Outsiders with Blaster and joining the Storm Fighters, Cori would-with Tails' help-design and create the wrist-com and mass produce it for his Teammates as well as the other two-legged Pokemon on the Storming Alliance. They would also come up with the upgrade for the wrist-com, calling the new design the Mega-com since items holding a Key Stone for Mega Evolution had the word "Mega" in it(Mega Ring, Mega Stickpin, etc.).
In The Legend of Fox the Brave: The wrist-com receives a somewhat minor explanation in Austin's Terror. It is mentioned that Austin tried and failed several times to get a call through to the Storm Fighters. Later, when Finitevus notices Austin's wrist-com when the warrior tries to shift his weight off his injured hip, he takes it off, snidely saying he didn't want Austin alerting his friends. Later, when Austin is taken to Dark Enerjak, the villain states that he was warned of the warrior's attempts to escape. He then says to never try it again; when Austin hesitantly asks what would happen, Enerjak coldly states that Austin knows before crushing the warrior's wrist-com easily. In Austin's Return, it's mentioned at the end that Austin received a new wrist-com from Cori after returning to the Storming Base. In the Prologue of Austin's Exile, it was mentioned that after the ambush, Silver and Diggs found Austin's ripped t-shirt and broken wrist-com. In Storm's Shadow, Austin's wrist-com is heard playing music when Storm enters Austin's room to speak with him after the warrior comes out of a coma and asks to speak with the young Buizel.
The wrist-com can also apparently be used as a music player, since in Storm's Shadow, Austin's wrist-com is playing the song Flawless when Storm enters Austin's room when the young dog asks to see him after coming out of a coma.