Roaming Guard

Roaming Guard is an open-source Android application in the System Tools category. It is designed to help prevent accidental mobile-data roaming by monitoring the mobile network operator to which the phone is connected. It is intended for Android users whose mobile plans require them to control which operators may be used, including users who want either warnings or attempted data blocking.

The app compares the current operator with a customizable MCC/MNC allowlist or denylist. It includes a predefined EU/EEA allowlist and lets users create a custom list that matches their mobile plan. When the phone connects to an unwanted operator, Roaming Guard can display a warning notification or, with some limitations, automatically block data traffic. The blocking function uses a local, on-device VPN service that drops traffic routed through the VPN. Android supports only one active VPN at a time, so using Roaming Guard alongside another VPN app may cause conflicts. Tethering and mobile hotspot traffic is not routed through this VPN and therefore cannot be blocked by it. System apps that explicitly choose their network connection may also bypass the VPN, while DNS and NTP traffic have been reported to leak outside it. Short periods after boot or when enabling the VPN may occur before traffic is filtered.

These limitations make the app’s blocking mode a device-level roaming control based on Android’s VPN mechanism, rather than a complete guarantee that every connection will be stopped. MirrorNest mirrors the official Roaming Guard build directly on its own storage and scans it for malware before publishing it. Its Android platform, open-source license, and System Tools classification place it among utilities concerned with controlling and monitoring core device networking behavior.