signal-watchapp

Signal on an Android (Wear OS) watch, built as a phone/watch pair. The watch never touches Signal's servers or crypto; the phone does all the work and the watch is a thin UI over the encrypted Bluetooth link.

Architecture (Tier 1 — notification bridge)

┌─────────────┐  notifications   ┌──────────────────┐  Wearable Data Layer  ┌───────────┐
│ Signal /    │ ───────────────► │ :phone           │ ◄───────────────────► │ :wear     │
│ Molly (app) │ ◄─────────────── │ SignalWear Bridge│   (MessageClient,     │ SignalWear│
└─────────────┘  RemoteInput     └──────────────────┘    BT, device-to-     └───────────┘
                 reply injection                          device only)

• :phone — a small bridge app (not a Signal fork). A NotificationListenerService mirrors Signal's MessagingStyle notifications into an in-memory conversation store; replies from the watch are injected back through the notification's own RemoteInput action, so Signal itself sends the message. Nothing extra talks to Signal's servers.
• :wear — Compose for Wear OS app: conversation list, message view, reply via the system voice/keyboard input, mark-as-read.
• :shared — JSON wire protocol between the two (kotlinx-serialization).

Both APKs share the net.deprekated.signalwear applicationId — the Wearable Data Layer only routes between same-package, same-signature apps. Debug builds of both are signed with the same debug keystore, so this works out of the box.

Known Tier 1 limitations (by design)

• Only conversations that produce notifications are visible; no deep history.
• Dismissing/reading a notification on the phone makes that conversation read-only on the watch until the next message arrives.
• Can't start a brand-new conversation from the watch.
• Message plaintext is mirrored to the watch (that's the point, but know it).

Tier 2 (planned): replace the notification bridge with a Molly-based fork running as a linked device, keeping this watch app and wire protocol unchanged — only the phone-side data source swaps.

Building

./gradlew :phone:assembleDebug :wear:assembleDebug

Requires JDK 17 and an Android SDK with platform 36 (local.properties points at ~/Android/Sdk).

Installing

1. adb install phone/build/outputs/apk/debug/phone-debug.apk (on the phone)
2. adb install wear/build/outputs/apk/debug/wear-debug.apk (on the watch — pair via adb pair / wireless debugging on the watch)
3. Open SignalWear Bridge on the phone and grant notification access.
4. Open SignalWear on the watch; conversations appear as Signal notifications arrive.