Transmit encrypted messages via sound — no Bluetooth, Wi-Fi, or data needed.
Audio-Based Secret Messaging App
Transmit encrypted messages via sound — no Bluetooth, Wi-Fi, or data needed.
Imagine two phones sitting next to each other — one sends a secret message through high-frequency sound (inaudible to humans), and the other decodes it through its microphone.
It’s like data transfer via sound waves, useful for:
- Offline data exchange
- Spy tools or fun secret chat
- Device pairing without network
- Classroom/study use for sneaky text transfer 😍
- Converts text into data packets.
- Modulates data as audio tones in the ultrasonic range (above normal human hearing).
- Sends tones through the phone speaker.
Example: 'HELLO' → binary → mapped to tones like 18000Hz, 18100Hz... etc.
- Before data transfer, devices do a quick tone handshake to sync.
- Could use a “ping” tone (like radar) to let the receiver know to start recording.
- Embed watermark/fingerprint into sound for authenticity.
- Could also help in error detection or app branding.
- Should work between:
- Android
↔️ Android - Android
↔️ Browser (via Web Audio API) - Browser
↔️ Browser
- Android
- Web app uses Web Audio API for both generating and analyzing ultrasonic sound.
- Android (Java/Kotlin) or Web (JS)
- Converts message to binary
- Maps binary → tone frequencies (FSK, ASK, or custom modulation)
- Plays modulated sound via speaker
- Listens using microphone
- Uses FFT (Fast Fourier Transform) to detect tone frequency
- Maps back from tone → binary → text
- Optional AES-128/256 or custom lightweight cipher
- Protects messages from being sniffed (e.g., if another mic is listening)
- Reed-Solomon ECC helps fix errors caused by noise
- Useful because ultrasonic waves can be affected by environment (walls, movement, etc.)
/secret-sound-messenger/
│
├── /android-app/ # Java app for mobile sender/receiver
│ └── AudioSender.java
│ └── AudioReceiver.java
│ └── ReedSolomon.java
│
├── /web-app/ # JS Web Audio app
│ └── encoder.js
│ └── decoder.js
│ └── visualizer.js
│
├── /core-algorithms/ # Shared modulation & encoding logic
│ └── modulation.py (or .js)
│ └── encryption.py
│
├── /docs/ # Documentation and tech explanations
│ └── signal-diagrams.png
│ └── protocol-spec.md
│
├── README.md
└── LICENSE
| Bit | Frequency |
|---|---|
| 0 | 18000 Hz |
| 1 | 19000 Hz |
| Sync | 20000 Hz |
- Each bit is played as a tone for a fixed duration (e.g., 50ms)
- Add start/stop tones to define boundaries
| Issue | Solution |
|---|---|
| Ambient noise | Use error correction (Reed-Solomon) |
| Devices have different speaker/mic quality | Dynamic calibration via handshake |
| Echo/overlap | Add delay between packets or unique “start tone” |
| Sound reflections in room | Use filtering and signal smoothing |
- 📷 Use QR codes to pair devices before sending (for added security)
- 📜 Chat history encryption + storage
- 🌍 Add a local-only offline chat history
- 📡 Add option to "broadcast" message to nearby phones
- 🧑🏫 Educational Mode: visualize the signal as a waveform
- Type your message
- App encrypts + encodes it to audio
- Plays high-frequency sound
- Opens mic in receive mode
- Listens for handshake tone
- Decodes sound to bits → text
- Decrypts and shows the message
This is perfect for GitHub because:
- It involves signal processing, encryption, low-level audio, and cross-platform logic
- Super unique, not many public repos like this
- You can write detailed documentation with visuals, diagrams, and live demos
This project is licensed under the MIT License.
Develope By - Sk Wasim Akram
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👨💻 All of my projects are available at https://skwasimakram.com
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📝 I regularly write articles on https://blog.skwasimakram.com
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📫 How to reach me hello@skwasimakram.com
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🧑💻 Google Developer Profile https://g.dev/skwasimakram
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📲 LinkedIn https://www.linkedin.com/in/sk-wasim-akram
