SackUp

Back up your phone to a USB drive — simple enough for your parents.

What is SackUp?

SackUp is an Android app that copies your phone's photos, videos, and files to a USB drive (SSD/flash drive) connected via a USB-OTG cable. It's built for people who aren't tech-savvy — your parents, grandparents, or anyone who just wants their files safe on a physical drive without fussing with cloud storage.

How It Works

First-Time Setup (done by you, the tech-savvy one)

1. Plug the USB drive into the phone with an OTG cable
2. Open SackUp and grant it access to the drive
3. The app comes with 3 backup groups ready to go: Camera, Downloads, and WhatsApp
4. For each group, you pick:
   • Phone folders — where files come from (e.g., DCIM, Pictures)
   • Drive folder — where files go (e.g., Camera-Backup)
5. Phone folder names are created inside the drive folder automatically:

Camera-Backup/
├── DCIM/
│   ├── IMG_001.jpg
│   └── IMG_002.jpg
└── Pictures/
    ├── Screenshot_01.png
    └── Screenshot_02.png

Everyday Use (what your parents do)

1. Plug in the USB drive
2. Open SackUp
3. Tap a backup group — that's it

Only new files are copied. When it's done: "12 files saved, 4.2 GB".

Freeing Up Phone Space

1. Tap the three-dot menu on a backup group
2. Tap "Free Up Space"
3. See how much space you'll get back
4. Confirm — only files safely on the drive get removed

Checking What's Backed Up

Tap "View Backed Up" on any backup group — works even without the drive plugged in.

Logs

A built-in log screen shows everything that happened — current session and previous sessions. Logs are copyable so you can paste them into a message if you need help troubleshooting.

Backup Engine

• Fast. Uses maximum CPU and I/O with large buffer sizes. No throttling. The phone is plugged in and doing one job — copy as fast as the USB connection allows.
• Runs in foreground and background. Backup keeps going if the user switches apps, locks the screen, or gets a phone call. A persistent notification shows progress the entire time.
• Progress is always visible. The notification shows which file is being copied and overall percentage. Inside the app, a full progress screen shows file count, current file name, and bytes transferred in real time.
• Only copies what's new. Before copying, the app scans the drive folder. Files already there (matched by name and size) are skipped. No wasted time re-copying.
• Picks up where it left off. If backup is interrupted (cable pulled, phone dies), just run it again. Already-copied files are skipped, and it resumes from where it stopped.
• Verifies every file. After copying, the app checks the file size on the drive matches the source. If it doesn't, the file is deleted and flagged — no silent corruption.
• Cancellable anytime. Cancel button in the notification and in the app. Stops after the current file. Partially copied files are cleaned up.
• Errors don't stop the job. If one file fails, it's skipped and reported at the end. The rest of the backup continues. The summary shows exactly what failed and why, in plain language.

Key Points

• Nothing gets deleted unless it's confirmed on the drive
• Works offline — no internet, no cloud, no accounts
• Big buttons, simple words — designed for people who find most apps overwhelming
• Fast — uses all available CPU to copy as quickly as the USB connection allows

Tech Stack

• Language: Kotlin
• UI: Jetpack Compose (Material 3)
• Storage: Android Storage Access Framework (SAF) for USB drive access
• Database: Room (backup groups, backup history, logs)
• Background work: Foreground Service with progress notification
• Min SDK: 26 (Android 8.0+)
• Target SDK: 35

Building

./gradlew assembleDebug

The debug APK will be at app/build/outputs/apk/debug/app-debug.apk.

Project Structure

app/src/main/java/com/sackup/
├── SackUpApp.kt              # Application class
├── MainActivity.kt           # Single activity, hosts Compose navigation
├── data/
│   ├── AppDatabase.kt        # Room database
│   ├── BackupGroup.kt        # Backup group entity + DAO
│   ├── LogEntry.kt           # Log entry entity + DAO
│   └── BackupRepository.kt   # Data access layer
├── service/
│   └── BackupService.kt      # Foreground service — the backup engine
├── ui/
│   ├── Navigation.kt         # App navigation graph
│   ├── HomeScreen.kt         # Main screen — list of backup groups
│   ├── SetupScreen.kt        # Configure a backup group
│   ├── ProgressScreen.kt     # Live backup progress
│   ├── LogScreen.kt          # View logs (copyable)
│   └── theme/
│       └── Theme.kt          # App theme
└── util/
    └── FileUtils.kt          # File size formatting, etc.

License

MIT