Multi-Profile App Locker -- Android App Lock with Separate PINs per User

Multi-Profile App Locker is an open-source Android app locker built with Flutter and Kotlin that lets two people share one device with complete app privacy. Each user creates their own profile with a separate 4-digit PIN, selects which apps to lock, and a native Kotlin Accessibility Service overlay blocks access until the correct PIN is entered.

Whether you're sharing a phone with a partner, a family member, or a roommate -- Multi-Profile App Locker gives each person their own locked app list, their own PIN, and their own privacy. No root required, no third-party lock engines -- just a native overlay powered by Android's Accessibility Service.

Key Features

• Multi-profile app locking -- two independent profiles on one device, each with its own name, emoji avatar, 4-digit PIN, and locked app list
• Native Kotlin lock overlay -- a TYPE_APPLICATION_OVERLAY window drawn on top of locked apps with profile picker and PIN pad; falls back to a dedicated LockActivity shown on lock screen
• SHA-256 PIN hashing -- PINs are never stored in plain text; hashed using the crypto package before writing to the database
• Brute-force protection -- 5 wrong PIN attempts trigger a 30-second lockout with shake animation feedback
• Categorized app selection -- browse all installed apps sorted by category (Social, Google, Entertainment, Other) with real-time search and selection counter
• Onboarding flow -- three-page introduction explaining the concept, followed by a step-by-step profile setup (avatar, name, PIN, confirm)
• Boot persistence -- a BootReceiver restores app lock protection automatically after device restarts
• Configurable re-lock timing -- set how long after unlocking an app before it locks again
• Dark & Light mode -- Material 3 themed UI and native overlay both respect the device theme
• Theme color customization -- pick a Material 3 seed color to personalize the entire app
• Change PIN flow -- update your PIN after verifying the current one; no way to bypass without the old PIN
• Danger zone -- full profile reset and uninstall protection options gated behind PIN verification
• Biometric unlock (planned) -- local_auth dependency is included; biometric authentication is declared in settings UI but not yet wired

Screenshots

How It Works

1. Create Profiles -- each user sets up a profile with a name, emoji avatar, and 4-digit PIN (hashed with SHA-256 before storage)
2. Select Apps -- browse installed apps by category, search by name, and toggle which apps to lock for that profile
3. Enable Protection -- grant Accessibility Service and overlay permissions; the native Kotlin service starts monitoring foreground app changes
4. Lock Triggered -- when a locked app is opened, the service checks the SQLite database and draws a full-screen overlay asking for the profile PIN
5. Unlock -- enter the correct PIN to dismiss the overlay; a configurable cooldown prevents immediate re-locking
6. Boot Recovery -- after a device restart, BootReceiver checks SharedPreferences and protection resumes automatically

Getting Started

Prerequisites

• Flutter SDK >= 3.11.0
• Android SDK
• A physical Android device (Accessibility Services do not work reliably on emulators)

Setup

git clone https://github.com/<your-username>/app_lock.git
cd app_lock
flutter pub get
flutter run

First Run

1. Grant overlay permission (SYSTEM_ALERT_WINDOW) when prompted
2. Enable the Accessibility Service in device settings -- the app guides you to the correct screen
3. Complete the onboarding and create your first profile with a 4-digit PIN
4. Select apps to lock, then open one of them to see the lock overlay in action

Android Permissions

Permission	Reason
SYSTEM_ALERT_WINDOW	Draw the PIN lock overlay on top of locked apps
RECEIVE_BOOT_COMPLETED	Restart protection automatically after device reboot
Accessibility Service	Detect foreground app changes in real time (user-granted in system settings)

Tech Stack

• Frontend: Flutter, Riverpod, Material 3, sqflite, SharedPreferences
• Native Layer: Kotlin, AccessibilityService, TYPE_APPLICATION_OVERLAY, SQLite
• Security: SHA-256 PIN hashing (crypto), 5-attempt lockout, PIN-gated settings
• Communication: MethodChannel (com.example.app_lock/service)

Use Cases

• Two partners sharing one Android phone who want separate app privacy
• Parents locking specific apps on a child's device with a different PIN than the child's own profile
• Roommates or family members sharing a tablet with individual locked app lists
• Anyone who wants per-profile app locking without rooting their device
• Developers looking for a reference implementation of Flutter + Kotlin Accessibility Service integration with overlay windows

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