CallBLuE

CallBLuE

BLuE is an Android app for offline voice calls over Bluetooth Low Energy: no SIM, Wi-Fi or mobile network needed. It also talks to Xiaomi's built-in "Offline Communication".

Independent project, not affiliated with Xiaomi. It contains no Xiaomi code; the protocol was documented through interoperability analysis.

• Calls between BLuE phones: long range on phones with LE Coded PHY, standard Bluetooth range otherwise. Encrypted, with a 4-digit check code on both screens.
• Xiaomi compatibility: optional and off by default. Xiaomi's format broadcasts your phone number openly, and BLuE warns about this.
• Native Android calls: ringing, lock screen, headsets, Mute and Speaker.
• Stay available: after opening BLuE and allowing Bluetooth, advertising and incoming calls continue off-screen. Listening resumes after unlocking following a reboot, or after an app update; the availability switch or notification's Go offline action turns it off. Nearby scanning runs while the app is open, with a short grace period when leaving.

Requires Android 8.0+ with Bluetooth Low Energy.

Keep Bluetooth on and allow call notifications to receive calls while the phone is locked. Background settings opens your phone's controls: on Xiaomi/POCO, enable BLuE under Settings → Apps → Background autostart; on other phones, allow background activity if their battery manager stops BLuE. Android's Force stop requires opening BLuE again.

Build

Install Android Studio with NDK (Side by side), then run gradlew assembleDebug. Run tests with gradlew testDebugUnitTest.

Docs

• Protocol

Licence

MIT. Bundles libspeex under its BSD licence (app/src/main/cpp/speex/COPYING).