The Venture Family use communicator watches to keep in touch with each other. Each member has one; Rusty, Brock, Hank, Dean and later Sgt. Hatred.
In All That And Gargantua 2, Billy mentions to Rusty that Hank gave him one of the watches as well which he had been told was a gift from Rusty but Rusty points out he had no idea, implying it was just an old watch he no longer needed.
In The Diving Bell vs. The Butter Glider, Brock finds out Hatred has his old communicator watch after he had shipped it back to Rusty from Argentina via a Mailboxes, Etc.
Hatred: I'm tired of you always "brock-blocking" me, Samson! I'm head of security! I'm the new sheriff of Venture Town! I wear the watch now!
Brock: That's my band. That's my watch band.