SignLock in Detail
SignLock is a unique drawing-based app locker for Android. Instead of PINs or patterns, you lock your apps with a personal drawing — something only you can replicate.
What is SignLock?
SignLock reimagines app security by replacing traditional PINs, patterns, and passwords with something more personal — your free-form drawing or signature.
When you open a protected app, SignLock presents a full-screen drawing canvas. Simply draw your signature to unlock. The app uses an advanced gesture recognition algorithm to match your drawing against your saved template, all processed locally on your device.
Fully offline and encrypted end-to-end on your device, SignLock ensures your privacy is never compromised.
Draw anywhere to unlock
How SignLock Works
A deep dive into the technology powering SignLock.
Gesture Recognition Engine
The core matching algorithm uses three weighted metrics: point distance similarity (40%) via bidirectional Chamfer distance, segment direction similarity (40%) using cosine similarity, and stroke length similarity (20%). Each stroke is resampled to 64 equidistant points for accurate comparison. Match threshold: 85%.
Android Keystore Encryption
Drawing templates and backup PINs are encrypted using AES-256/GCM/NoPadding via the Android Keystore system. The encryption key is hardware-backed and never exposed to the application layer. Decrypted only in memory for matching, then securely discarded.
Accessibility Service Integration
SignLock uses Android's Accessibility Service to monitor window state changes. When a protected app opens, the service triggers the lock screen overlay. The service runs efficiently in the background with minimal battery impact.
Overlay Lock Screen
The unlock screen is rendered as a full-screen WindowManager overlay using Jetpack Compose. It covers the locked app completely, including the status bar. FLAG_SECURE is set to prevent screenshots and screen recording.
Session & Grace Period Management
After unlocking, a grace period (1.5s) prevents re-locking during rapid app switching. A cooldown period (2s) activates after each unlock. When the screen turns off, all unlock state is cleared, requiring re-authentication.
Multi-Device Compatibility
Built with Jetpack Compose and Material 3 for modern Android devices. Supports both portrait and landscape orientations. Special handling for Samsung One UI battery optimization to ensure reliable background operation.
Complete User Journey
Onboarding
Welcome screen introducing SignLock's core value: drawing-based app protection. Users learn about the fully offline, privacy-first approach.
Permissions Setup
Two required permissions: Accessibility Service (to detect protected apps) and battery optimization exemption (to keep the service running reliably). Real-time status badges show grant progress.
App Selection
Searchable list of all installed apps. Users tap to select which apps to protect. Selected apps show a checkmark. An accessibility gate prevents proceeding if the service is disabled.
Drawing Password Creation
Full-screen drawing canvas. Users draw any pattern or signature. The drawing must meet minimum size requirements (40px bounding box, 30px path length). Undo and Clear options available.
Drawing Confirmation (Two Steps)
Users draw their pattern twice more for consistency. The GestureRecognizer matches each drawing against the provisional template. On failure, a pattern guide hint appears. On success, the template is encrypted and saved.
Backup PIN Setup
Users choose between 4 or 6-digit PIN length. Enter the PIN using a custom keypad. Animated shake on error. PIN is encrypted via Android Keystore and stored in Room database.
Dashboard & Management
Four-tab dashboard: Apps (manage protected apps), Security (lock policies, privacy mode, change password/PIN), Themes (drawing themes, background themes), Settings (wallpaper, accessibility, app info, reset).
The Unlock Experience
Drawing Mode
- Full-screen drawing canvas
- Supports complex multi-stroke drawings
- Real-time stroke rendering with glow effects
- Privacy mode hides strokes as you draw
- Clear button to restart
- Switch to backup PIN option
- 30-second lockout after too many failures
PIN Mode
- Custom numeric keypad (0-9)
- Submit and backspace buttons
- PIN dots indicator
- Animated shake on incorrect PIN
- Switch to drawing mode option
- Same 30-second lockout protection
- 4 or 6-digit PIN support
Auto-Unlock Animation
- Checkmark animation on successful unlock
- Scale-down and fade-out transition
- Returns seamlessly to the locked app
- Grace period prevents re-locking (1.5s)
- Cooldown between unlock attempts (2s)
- Screen-off clears all unlock state
- Supports both portrait and landscape
Get SignLock
SignLock is available on Google Play. Download it today and secure your apps with your signature.