Reiki Session — Wear OS interval timer for Pixel Watch 3

A quiet, eyes‑closed interval timer for Reiki and meditation sessions, built for the Pixel Watch 3 (Wear OS 5). You pick two things — how long the whole session lasts and how long to hold each hand position — and the watch gently buzzes on every position change and again, more firmly, when the session ends. No position names, no numbers, no fuss: just two countdowns and your hands.

The timer runs in a foreground service with a wake lock, so the cues keep coming even when the screen is off and the watch is dozing — exactly what you need when your eyes are closed and your wrist is resting.

Features

• Two simple dials — session length and per‑position length, with a live hint of how many positions fit (e.g. 10 positions).
• Dual countdowns during a session — time left on the current position (large) and time left in the whole session (below).
• Distinct haptics — a double "heartbeat" buzz on each position change, and three strong half‑second pulses at the very end.
• Pause / Stop — pause both countdowns (handy when a client turns over from back to front); stop ends the session and shows the summary.
• Shake to pause — a firm wrist shake toggles pause without opening the screen.
• Heart‑rate summary — optional. A Fitbit‑style "Done" screen reports duration, positions, average / minimum BPM and start → end heart rate.
• Keep screen on — optional, for when you want the display to stay lit.
• Drift‑free timing — the timer is anchored to wall‑clock time, so it stays accurate even when the app is backgrounded and the CPU sleeps.
• Settings — keep‑screen‑on, heart rate, linked vs independent session math, and default position / session durations, all persisted between runs.

Linked vs independent sessions

The Session by positions setting controls how the two dials relate:

• On (linked) — the session length is always a whole number of positions. Stepping the session moves it one position at a time; changing the position re‑snaps the session to a clean multiple. The hint reads e.g. 10 positions.
• Off (independent) — session and position are set separately (session steps by one minute). The number of positions is rounded up and shown as ≈ N.

How it works

• SessionService — a foreground service (foregroundServiceType="health") that owns the timer, holds a PARTIAL_WAKE_LOCK, drives the Vibrator, and publishes session state the UI observes. Because it's a foreground service with a wake lock, vibration cues survive screen‑off and Doze.
• Drift‑free timer — elapsed time is computed from SystemClock.elapsedRealtime anchors (start time, accumulated pause time) rather than counting ticks, so a backgrounded session never runs long.
• Heart rate — captured through Health Services ExerciseClient (HEART_RATE_BPM). Health Connect is unavailable on the watch, so a lightweight Health Services workout is used purely to sample BPM for the summary.
• Shake detection — ShakeDetector watches the accelerometer for a burst of spikes above a g‑force threshold within a short window, with a cooldown.
• UI — Jetpack Compose for Wear OS. The whole app is three screens: setup, running session, and the post‑session summary, plus a settings screen reached by the gear button below the setup screen (swipe right to leave without saving).

Tech stack

Kotlin · Jetpack Compose for Wear OS · Health Services Client · Foreground service

• wake lock · SharedPreferences.

compileSdk 35 · minSdk 30 · targetSdk 34 · AGP 8.5.2 · Kotlin 1.9.24 · Gradle 8.7 · JDK 17 (Temurin).

Project structure

app/src/main/java/com/pavel/reikitimer/
  MainActivity.kt     Compose host: setup screen, settings screen, navigation
  SessionScreen.kt    Running‑session UI + Fitbit‑style summary
  SessionService.kt   Foreground service: timer, wake lock, vibration, heart rate
  SessionState.kt     Observable UI state + summary model
  SessionMath.kt      Pure timing math (positions, clamping, snapping)
  TimeFormat.kt       mm:ss / h:mm:ss formatting
  ShakeDetector.kt    Accelerometer shake-to-pause
  Settings.kt         Settings data class
  SettingsStore.kt    SharedPreferences persistence
app/src/test/java/    JVM + Robolectric unit tests
docs/                 Design notes and screenshots

Build

./build.sh    # debug APK -> app/build/outputs/apk/debug/app-debug.apk

build.sh sources env.sh (which sets JAVA_HOME / ANDROID_HOME) and runs ./gradlew assembleDebug.

Install on Pixel Watch 3

The watch has no data USB port, so install over Wi‑Fi (Mac and watch on the same network). On the watch: Settings → System → About → tap Build number ×7 → Developer options → enable ADB debugging and Wireless debugging → Pair new device (this shows an IP:port and a pairing code).

./deploy-watch.sh pair    <IP:PAIRING_PORT> <CODE>   # once
./deploy-watch.sh install <IP:DEBUG_PORT>            # IP:port from the Wireless debugging page

The debug port rotates each time wireless debugging reconnects — read the current one from the Wireless debugging screen. Turn wireless debugging off afterwards to save battery.

Emulator

source env.sh && emulator -avd reiki_wear   # Wear OS 5, arm64

Tests

./gradlew testDebugUnitTest

Two tiers: pure‑JVM logic tests (timing math, formatting, shake detection, UI state) and Robolectric tests for Android‑dependent pieces — 30 tests across SessionMathTest, SessionUiStateTest, TimeFormatTest, ShakeDetectorTest, SettingsStoreTest, and SessionServiceTest.

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A personal project, shared in case it's useful to other Reiki and meditation practitioners. The violet hands icon nods to the crown‑chakra colour often used to depict Reiki energy.