I'm thinking the Mallers are using police/fire fighter radios. I'm just guessing because Tardust appears to be in charge of listening to the Tower's CB frequencies, but he also mentions that Bricks and he encounted a biter at the police station. He doesn't say what they were doing at the police station but I'm assuming that they might have been able to pick up a few police radios while there. They definitely aren't using CB's to communicate with each other, but they are listening.