StealthCalc appears to be a beautifully designed, functional calculator. But beneath the surface lies a secure, encrypted vault for your private notes.
Engineered with Modern Android Development (MAD) standards, this app demonstrates how to blend utility with security. It features a cyberpunk-inspired aesthetic, fluid Edge-to-Edge transitions, and industry-standard biometric authentication.
"Hidden in plain sight." — A privacy tool that doesn't look like one.
- Fully Functional Engine: Powered by
exp4jfor complex arithmetic (+,-,*,/,%). - Smart History: A scrollable tape logs your calculations in real-time.
- Immersive UI: A stunning "Cyberpunk" gradient interface that draws behind system bars.
- The Trigger: Enter the access code
69/67and press=to initiate the unlock sequence. - Biometric Gate: Hardware-backed Fingerprint / Face ID authentication prevents unauthorized access.
- Persistent Storage: Notes are securely stored using a local Room Database.
- Masonry Grid: Notes are displayed in a staggered, dynamic grid (similar to Google Keep).
- Gesture Control: Swipe-to-delete notes with haptic feedback and undo animations.
- Adaptive Contrast: The note editor automatically adjusts text color (Black/White) based on the background luminance for perfect readability.
- Fluid Navigation: Custom entry/exit animations make the vault feel like a physical hidden layer.
| The Disguise | The Unlock | The Vault | The Editor |
|---|---|---|---|
 |
 |
 |
 |
Built entirely with Kotlin and the latest Jetpack libraries.
| Layer | Component | Technology Used |
|---|---|---|
| 🎨 UI | Design System | Jetpack Compose (Material 3) |
| Animations | Compose Animation API (Shared Transitions) | |
| Immersion | Edge-to-Edge API | |
| 🧠 Logic | Architecture | MVVM + Clean Architecture principles |
| DI | Dagger Hilt | |
| Concurrency | Coroutines & Kotlin Flows | |
| 💾 Data | Local DB | Room (SQLite Abstraction) |
| Math Engine | exp4j | |
| 🛡️ Security | Auth | Android Biometric API |
StealthCalc follows a strict Unidirectional Data Flow (UDF) and separation of concerns.
graph TD
UI[Compose UI Layer] <-->|Events & State| VM[ViewModel]
VM <-->|Use Cases| Repo[Repository]
Repo <-->|SQL Queries| Room[Room Database]
Repo <-->|Auth Request| Bio[Biometric Manager]
com.fury.stealthcalc
├── data # Room Entities, DAOs, and Database config
├── di # Hilt Dependency Injection Modules
├── presentation # UI Layer
│ ├── calculator # Calculator Logic & State
│ ├── vault # Staggered Grid & Gestures
│ └── add_edit # Adaptive Color Logic
├── ui.theme # Custom Typography & Color Systems
└── domain # (Optional) Business Logic & Use Cases
NOTE: — Biometric must be enabled on your device.
Download the App:
- Click below to download the latest stable version (v1.0.1) for your Android device:
- 👉 Download StealthCalc-v1.0.1.apk
OR
To explore the code or build it yourself:
-
Clone the repository
git clone https://github.com/SilentFURY-x/StealthCalc-Secret-Notes-Calculator-App.git
-
Open in Android Studio
- Ensure you are using Android Studio Koala or newer.
- Minimum SDK: API 26 (Android 8.0).
-
Build & Run
- Sync Gradle.
- Select app configuration.
- Run on an Emulator (with Fingerprint enabled) or Physical Device.
Contributions are what make the open-source community such an amazing place to learn, inspire, and create. Any contributions you make are greatly appreciated.
-
Fork the Project
-
Create your Feature Branch:
git checkout -b feature/AmazingFeature
-
Commit your Changes:
git commit -m 'Add some AmazingFeature' -
Push to the Branch:
git push origin feature/AmazingFeature
-
Open a Pull Request
Arjun Tyagi
"🔐 Real security is not just about strong locks, but about not knowing there is a door at all."