Altitude Alert

An Android app for balloon pilots that monitors altitude in real time and fires configurable alerts when crossing set altitude limits.

Features

• Altitude band alerts — set a lower and upper altitude limit; the app alerts when approaching or crossing either edge
• Approach alert — three beeps when within a configurable distance of a band edge
• Crossing alarm — continuous two-tone alarm when outside the band; can be muted from the notification or main screen
• Max altitude alert — continuous alarm when approaching the balloon's all-time session maximum altitude
• Dual altitude source — fuses barometer (when available) and GPS; falls back to GPS-only automatically
• Altitude units — display in feet, metres, or flight levels
• Foreground service — monitoring continues with the app in the background
• Persistent config — all settings survive app restarts

Requirements

• Android 13 (API 33) or higher
• Location permission (fine + coarse)
• Notification permission
• Barometer sensor is optional; GPS is always used

Screenshots

TODO

Architecture

Data flows top to bottom through four layers:

FusedAltitudeDataSource  ──►  AltitudeMonitor  ──►  MonitorService  ──►  MainViewModel  ──►  UI
      (sensor/GPS)            (pure domain)          (foreground svc)      (StateFlow)       (Compose)

• FusedAltitudeDataSource — merges barometer (SensorManager) and GPS (FusedLocationProviderClient) into a single AltitudeReading flow. GPS readings time out after 10 s of silence.
• AltitudeMonitor — pure, Android-free domain class. AlertEngine classifies each reading as CLEAR / APPROACHING / CROSSED for both limits.
• MonitorService — bound + started foreground service. Owns the monitor, drives the alarm sound and vibration, and posts status notifications. State is exposed via MonitorBinder as StateFlows.
• MainViewModel — binds to the service, merges binder flows into a single MainUiState, and persists config changes immediately via ConfigRepository.
• UI — two Compose screens (MainScreen, AdvancedSettingsScreen) switched via an AppScreen enum; no Jetpack Navigation dependency.

Dependencies are wired manually — no DI framework is used.

Package Structure

Package	Contents
data/model	AlertConfig, MaxAltitudeConfig, AltitudeReading
data/source	AltitudeDataSource interface + FusedAltitudeDataSource
data/repository	ConfigRepository, DataStoreConfigRepository, SystemInfoRepository
domain	AltitudeMonitor, AlertEngine, MonitorState, AlertResult
service	MonitorService, AlarmSoundPlayer, AlarmVibrator
notification	MonitorNotification, MonitorStatusFormatter
ui	MainViewModel, MainScreen, AdvancedSettingsScreen, MainAction, Validation
ui/theme	Compose theme, colors, typography
util	AltitudeConverter (barometric formula, metres ↔ feet, flight levels)

Tech Stack

• Kotlin + Jetpack Compose + Material 3
• Kotlin Coroutines / Flow
• AndroidX DataStore (config persistence, JSON-serialised via kotlinx.serialization)
• Google Play Services Location (FusedLocationProviderClient)