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Power-saving strategy (Android-only)

This project only ships to Android. Every battery decision below is enforced both in the JS facades (libs/services/*) and in the Kotlin Nitro implementations under android/src/main/java/.../mibandactive/ (to be authored).

Non-negotiables

  1. No always-on foreground service. A foreground service is started only during an active sync window (≤ 60s typical) and stopped immediately when the sync resolves. Connecting → syncing → disconnect is one atomic job.
  2. No WAKE_LOCK. WorkManager wakes the device for us. We never pin the CPU on ourselves.
  3. No background location permission. Android's BLE-scan needs ACCESS_FINE_LOCATION only while in foreground. We do not request ACCESS_BACKGROUND_LOCATION.
  4. Periodic sync interval ≥ 30 min (PeriodicWorkRequest, minimum 15 min by Android rules, we use 30). User can extend this but cannot shorten below 30 min.
  5. Realtime HR streaming OFF by default. It is the single biggest power sink on the band and on the phone radio. Users must explicitly opt in per-session.

BLE scan policy

Phase Duration Duty cycle Window
Onboarding scan (foreground) 12 s max continuous one-shot
Auto-reconnect (background, screen off) 1.2 s active / 12 s idle ≤ 10% only during scheduled work window
Manual re-pair 12 s max continuous user-triggered

We never start a background BluetoothLeScanner that runs > 15 s. The Kotlin implementation must call stopScan() on a Handler-posted timeout, not on the assumption the OS will preempt.

WorkManager schedule

Job Cadence Constraints
DailySummarySyncWorker every 30 min (periodic) requiresBatteryNotLow=true, no network constraint
NotificationFlushWorker one-time, expedited, on NLS event setExpedited() only when band is already connected; otherwise enqueue normal
WeatherPushWorker every 6h requiresBatteryNotLow=true, network connected
CalendarPushWorker every 6h requiresBatteryNotLow=true

requiresBatteryNotLow=true means: when the phone is under 15% battery, we skip the run. The user can still pull-to-refresh manually on the dashboard.

Doze / App Standby

We assume Doze. We do not ask for "Ignore battery optimization" in the onboarding flow (it's a soft prompt only, skip is OK). The work pattern is designed to fire during maintenance windows that Doze itself grants.

If the OEM is aggressive (MIUI, ColorOS, EMUI), we let the user know via an in-app banner: "你的廠商可能會在背景殺掉同步,設定 → 電池 → 不限制本 App / Your OEM may kill background sync — exempt this app in system settings."

Notification forwarding

NotificationListenerService callbacks are short. We:

  • Drop notifications that are not in the user's allow-list before waking the BLE stack.
  • Coalesce a 250ms window of incoming notifications into a single BLE write.
  • Downscale notification icons to 24×24 PNG before send (Gadgetbridge sends 40×40+; we save flash + RF time).

What we do NOT do (and won't add)

  • ❌ Persistent foreground service "for reliability".
  • ❌ JobIntentService, AlarmManager.setExactAndAllowWhileIdle() polling loops.
  • ❌ Background BLE scan with SCAN_MODE_LOW_LATENCY.
  • ❌ Continuous heart-rate streaming as the default.
  • ❌ Asking for ACCESS_BACKGROUND_LOCATION.

Auditing

There's a Logcat tag prefix MB9A_POWER on every wake-up. Run adb shell dumpsys batterystats after a 24h soak to verify the per-app wake count stays under 50.