Intratone Auto-Open

React Native app that automatically answers your Intratone intercom call, listens for DTMF digits, and presses # (or your chosen key) when the correct code is entered — unlocking the door hands-free.

How it works

Visitor dials your apartment on the intercom
  → Intercom calls your phone
    → App auto-answers (Android only)
      → Visitor enters digicode on intercom keypad
        → App detects DTMF tones via Goertzel algorithm
          → If code matches → app presses # to open the door

Platform support

Feature	Android	iOS
Detect incoming call	✅	✅ (CallKit)
Auto-answer specific number	✅	❌
DTMF tone detection	✅ (Goertzel)	❌
Auto-press trigger key	✅	❌

Android is the primary target. iOS is stubbed with the same JS interface for future implementation via CallKit + local notifications.

Setup

Prerequisites

• Node.js 18+
• Android Studio with SDK 34+
• Android device (emulator won't simulate real calls)
• React Native dev environment: https://reactnative.dev/docs/environment-setup

Install

cd IntratoneAutoOpen
npm install

Run on Android

# Connect your Android device via USB (with USB debugging enabled)
npx react-native run-android

Required Android setup (one-time)

After installing the app on your device:

1. Grant all permissions — the app will prompt on first start
2. Set as default phone app — Settings → Apps → Default Apps → Phone app → Intratone Auto-Open
3. This is required for InCallService to intercept calls

Configuration

In the app:

• Numéro de l'interphone — the phone number that your Intratone intercom calls from (e.g. +33123456789)
• Code d'ouverture — the fixed code visitors must enter (e.g. 1234)
• Touche de déclenchement — which key to press when code matches (default #)

Architecture

src/NativeIntercomModule.ts      ← Turbo Module spec (JS interface)
App.tsx                          ← UI: settings + live status + log

android/.../IntercomModule.kt    ← Native module: config, DTMF handling, events
android/.../IntercomCallService.kt ← InCallService: call interception, auto-answer
android/.../DTMFDetector.kt      ← Goertzel algorithm for DTMF tone detection
android/.../IntercomPackage.kt   ← Turbo React package registration

ios/.../IntercomModule.m         ← iOS stub (CallKit detection only)

DTMF Detection

Uses the Goertzel algorithm to detect DTMF frequency pairs from the call audio stream. More efficient than FFT since it only checks 8 specific frequencies:

• Low: 697, 770, 852, 941 Hz
• High: 1209, 1336, 1477, 1633 Hz

Digit map:

        1209  1336  1477  1633
697:    1     2     3     A
770:    4     5     6     B
852:    7     8     9     C
941:    *     0     #     D

The detector runs on a background thread, reads from VOICE_DOWNLINK audio source (incoming call audio), processes 205-sample blocks (~25ms at 8kHz), and uses debouncing to avoid duplicate detections.

Limitations

• Android only for full auto functionality
• Requires being set as default phone app
• VOICE_DOWNLINK audio source availability varies by device/Android version — falls back to VOICE_CALL
• Minimum Android 8.0 (API 26) for InCallService.playDtmfTone()