Completed hardware/software side project turning an old Sony Xperia Z3 Compact into a dedicated Tamagotchi-style monster handheld.
Cryptid Pet is a single-file HTML5 virtual pet and arcade system packaged into an Android APK for a 2014 Sony Xperia Z3 Compact running Android 6. The goal was not to publish a mobile game, but to downgrade a modern-feeling interactive pet system far enough to run reliably on obsolete smartphone hardware.
The final APK runs fullscreen, hides the normal Android navigation UI, keeps the screen awake, registers as launcher and makes the Z3 behave like a dedicated Cryptid Pet device instead of a normal phone.
Main Pet Interface |
Device Wallpaper Result |
Visual Concept |
Completed private device project. No Play Store, App Store, Zepp Store or public release is planned.
Target hardware:
- Sony Xperia Z3 Compact
- Released: 2014
- Android 6.0.1 Marshmallow
- 4.6" 720×1280 display
- Qualcomm Snapdragon 801
- 2 GB RAM
- Project layout target: 360×640 portrait WebView
- Offline-first local gameplay
- APK-based dedicated-device setup
- Single-file HTML5 app packaged as Android APK
- Custom Android WebView wrapper instead of Capacitor
- Android 6 / old WebView compatibility work
- Dynamic SVG monster rendering with visual mutations
- Local save/load system
- Pet stats, feeding, sleeping, healing, expeditions and room progression
- Hardware step detector integration
- Reactions to real-world movement, shaking and time of day
- Native Android home/lock screen wallpaper support
- Built-in arcade with pet economy rewards
- Manual Zepp OS watchface export experiment
The pet has hunger, happiness, energy, hygiene and HP stats. It can level up, evolve, mutate visually, go on expeditions, unlock furniture and react to device context.
The goal was to make the app feel like a small living object, not just a webpage running on a phone.
The pet can react to real-world and device context:
- Steps and movement
- Strong shaking
- Time of day
- Device-context hooks
- Wallpaper/device presence outside the app itself
All arcade games are connected to the pet economy through points, wins, rewards or progression hooks.
Included mini-games
- Brick Breaker
- Battleship
- Artillery
- Connect Four
- Tic Tac Toe
- Othello / Reversi
- Minesweeper
- Blockfall
- Color Match
- Pong
- Void Dash
- Void Drift
- Star Siege
- Blast Zone
- Neon Grid
- Void Snake
- Nebula Storm
- Bubble Burst
Capacitor was tested first, but the Android 6 WebView was too old and unreliable for that bridge. The final APK uses a simpler custom WebView shell with only the native hooks that were actually needed.
Implemented Android-side behavior:
- Fullscreen immersive mode
- Hidden navigation/system UI
- Keep-screen-on flag
- Launcher registration
- Hardware step detector support
- Native wallpaper setter for home and lock screen
- Custom app icon
An Amazfit GTR 3 Pro / Zepp OS watchface was built as an external experiment.
The pipeline used the current evolving monster appearance, generated animated frames from it, rebuilt the watchface and installed it manually through the Zepp developer bridge.
Automatic watchface updates were not practical because of Zepp OS, bridge and side-service limitations. The watchface is therefore documented as a successful technical experiment, not as a finished user feature.
- HTML5 / CSS / Vanilla JavaScript
- SVG monster rendering
- Canvas mini-games
- localStorage persistence
- Android WebView
- Native Android sensor hooks
- Native Android wallpaper API
- Python helper scripts
- Zepp OS JavaScript
- Node / Zeus CLI
DEVLOG_SUMMARY.md— project history and development decisionsTECHNICAL_NOTES.md— Android 6, WebView, sensors and rendering notesWATCHFACE_EXPERIMENT.md— manual Amazfit watchface pipeline
This project moves in the opposite direction of most modern app development.
Instead of adding a large framework and targeting current devices, it takes modern interaction patterns and forces them onto an old Android 6 phone. Most of the real work was making the app feel smooth and alive despite old WebView limits, missing browser features, weak hardware and a tiny portrait display.
The result is a dedicated pocket pet device built from an obsolete smartphone.