Pocket Butler – Anti-Theft Security App

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  home

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  trusted device selection screen

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  armed

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  lock

Inspiration

Smartphone theft is common, and most anti-theft apps fail once the thief powers off the phone or lowers the volume. I wanted to build a solution that cannot be silenced easily and continues protecting the device even during shutdown attempts.

What it does

Pocket Butler is an Android anti-theft security app that triggers a loud alarm and vibration when a trusted Bluetooth device disconnects. It locks the volume at maximum, prevents shutdown attempts using accessibility-based protection, and requires a PIN to disarm.

How we built it

The app is built using Flutter for the UI and Android native Kotlin for system-level features. I integrated Bluetooth monitoring, a native vibration service, volume locking, overlay security, and an Accessibility Service to block shutdown actions. Flutter communicates with native services using MethodChannels.

Challenges we ran into

The biggest challenge was preventing shutdown on modern Android versions due to system restrictions. Broadcasts and overlays were unreliable on some devices, so I implemented an accessibility-based fallback that instantly dismisses the power menu. Managing multiple native services without conflicts was also challenging.

Accomplishments that we're proud of

• Built a reliable anti-theft system that continues working even when a thief tries to silence the phone or power it off.
• Successfully implemented an Accessibility Service to actively prevent shutdown attempts on modern Android versions.
• Achieved seamless Flutter ↔ native Android (Kotlin) integration using MethodChannels for system-level control.
• Designed a single-source-of-truth architecture for alarm, vibration, and volume locking to avoid conflicts and bugs.
• Ensured the app works across different OEM devices by handling Android security and permission limitations correctly.

What we learned

I gained deep experience with Android system internals, Accessibility Services, Flutter–Kotlin interoperability, and designing resilient security-focused architectures that work across different OEM devices.

What's next for Pocket Butler – Anti-Theft Security App

• Add remote control features such as triggering alarms, locking the device, or tracking location from another phone.
• Implement cloud backup and real-time notifications when theft is detected.
• Expand protection modes using motion sensors and geofencing.
• Improve UI/UX and onboarding to make security setup easier for non-technical users.
• Prepare the app for Play Store release with compliance, performance optimizations, and wider device testing.

Built With

• accessibility-service
• android-(kotlin)
• android-foreground-services
• bluetooth-apis
• dart
• flutter
• methodchannel
• vibrationeffect