In Star Trek: The Next Generation, DS9, and Voyager, it seems common for officers to touch their communicators to initiate a conversation but it's unclear when the person on the other side stops listening and can't hear them.
Granted sometimes it's as simple as a verbal close ("Picard Out", "Acknowledge Enterprise") but other times, the characters will just stop talking to the remote party and resume another conversation with someone nearby.
Is there an in-universe explanation for how this technology terminates a long-range conversation? Are communicators using AI to determine whether or not a given conversation is relevant? Or is it assumed that the remote party is manually terminating the conversation?