A visibility boundary is the line between information meant only for the device owner and information that can be seen by other people or systems. In user interfaces, this can depend on where data appears: a locked screen, shared dashboard, notification banner, or public status display. Even low-risk data, such as battery level or connection status, can become a privacy issue when it is placed in a highly visible location.
In cyber security, visibility boundaries matter because attackers often exploit what is exposed at a glance. A screen visible in an office, classroom, or shared home can reveal device presence, user routines, or operational state. Defenders manage this by limiting lock-screen details, applying role-based display rules, and offering settings that reduce accidental disclosure. The goal is not only to protect data from theft, but also to control who can observe it in the first place.