Seb3thehacker 043dc11251 Add phone call handling on the car screen
Incoming calls now show the caller (name via contacts, else number) on
the car UI with answer/decline, using a call screening service so the
car sees a call before it rings. Also adds pinnable nav bar shortcuts,
lowers minSdk to 31 for wider device support, and bumps to 0.0.04-pre.
2026-09-26 11:43:09 -07:00

Gearslip icon

Gearslip

Bring any app to your car screen.

What Gearslip is

Gearslip is an Android Auto client for the phone. It speaks the Android Auto protocol directly to a car head unit over USB, with no Google software in the path. Gearslip acts as a Car App Library host: an app that ships a car interface hands Gearslip a template, and Gearslip renders that template natively on the car screen. Nothing is mirrored from the phone. For apps without a car interface, Gearslip offers a separate screen-sharing mode.

The author reverse-engineered the protocol for interoperability, so that a client other than Google's own can talk to a car head unit.

Status

  • Templated apps work. Gearslip renders all 16 template types that the Car App Library defines, and it draws its own keyboard for search and sign-in. It has been tested against several real navigation and media apps.
  • Media playback works. Gearslip lets you browse and control car-enabled media apps from the car screen, with lyrics and playback state, over the same host connection.
  • Audio reaches the car by capturing playback, not by mirroring the screen. Android requires a screen-share style consent dialog and indicator for this, even though Gearslip never reads the screen; that grant is the only way a non-privileged app can tap another app's audio. The consent normally repeats every drive; the app's own setup steps include two optional adb commands that reduce it to a one-time grant.
  • A real head unit needs a certificate that Google controls. A head unit accepts only a phone identity that chains to Google's Automotive Link certificate authority, and Google alone issues those certificates. Gearslip does not ship one. Without it, Gearslip runs and renders correctly against a debug harness, but a real car rejects the connection. A leaked certificate exists that older head units accept; newer firmware and Google's reference tooling reject it.
  • Gearslip needs no adb, root, or Shizuku. Every feature relies on an ordinary Android permission or an on-device consent dialog. The two adb commands mentioned above, for audio, are the sole exception: both are optional, and both only remove a dialog that the driver would otherwise see once per drive.

Building

./gradlew :gearslip:assembleDebug

The APK lands at build/Gearslip-debug.apk.

A release build needs a signing key. Copy keystore.properties.example to keystore.properties, fill in your own values, and run ./gradlew :gearslip:assembleRelease. Git ignores both the properties file and the keystore. Without them, the debug build still works.

Writing apps for Gearslip

docs/BUILDING_APPS.md specifies how to write apps that Gearslip can render: templated apps, media apps, and the Gearslip app protocol.

License

Gearslip is licensed under AGPL-3.0; see LICENSE. The author offers a separate commercial license for private use outside the AGPL's terms; see NOTICE.md.

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