When the "Allow modifying system settings" permission (android.permission.WRITE_SECURE_SETTINGS) is granted on an Android device (typically via ADB or root access), apps can interact with system-level settings that are normally restricted. Here are some practical examples of what can be done with this permission:

1. Display Settings

• Change screen brightness programmatically:
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  Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, 255);

• Toggle auto-rotate:
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  Settings.System.putInt(getContentResolver(), Settings.System.ACCELEROMETER_ROTATION, 1);

• Adjust screen timeout:
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  Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_OFF_TIMEOUT, 30000); // 30 seconds

2. Sound and Volume

• Set media/ringer/alarm volume:
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  AudioManager audioManager = (AudioManager) getSystemService(AUDIO_SERVICE);
  audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, 15, 0);

• Enable/disable Do Not Disturb mode:
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  NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
  notificationManager.setInterruptionFilter(NotificationManager.INTERRUPTION_FILTER_NONE);

3. Network and Connectivity

• Toggle Wi-Fi:
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  WifiManager wifiManager = (WifiManager) getSystemService(WIFI_SERVICE);
  wifiManager.setWifiEnabled(true);

• Change mobile data state (requires additional permissions):
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  ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
  connectivityManager.setMobileDataEnabled(true);

4. System UI and Navigation

• Hide navigation bar:
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  Settings.Global.putInt(getContentResolver(), "force_fsg_nav_bar", 0);

• Enable/disable immersive mode (fullscreen):
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  getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);

5. Device Identification

• Change device hostname (requires root):
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  Settings.Global.putString(getContentResolver(), Settings.Global.DEVICE_NAME, "NewHostname");

6. Development and Debugging

• Enable USB debugging programmatically:
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  Settings.Global.putInt(getContentResolver(), Settings.Global.ADB_ENABLED, 1);

• Toggle "Stay awake" (screen never sleeps while charging):
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  Settings.Global.putInt(getContentResolver(), Settings.Global.STAY_ON_WHILE_PLUGGED_IN, BatteryManager.BATTERY_PLUGGED_AC);

7. Accessibility

• Enable/disable accessibility services:
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  Settings.Secure.putString(getContentResolver(), Settings.Secure.ENABLED_ACCESSIBILITY_SERVICES, "com.example/.MyAccessibilityService");

8. Location Settings

• Toggle GPS:
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  Settings.Secure.putInt(getContentResolver(), Settings.Secure.LOCATION_MODE, Settings.Secure.LOCATION_MODE_HIGH_ACCURACY);

9. Battery and Performance

• Enable/disable battery optimization for specific apps:
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  PowerManager powerManager = (PowerManager) getSystemService(POWER_SERVICE);
  powerManager.setIgnoringBatteryOptimizations("com.example.app", true);

10. Input Methods

• Change default keyboard:
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  Settings.Secure.putString(getContentResolver(), Settings.Secure.DEFAULT_INPUT_METHOD, "com.example.keyboard/.MyIME");

Important Notes:

• Security Risks: Modifying system settings can destabilize the device or expose it to security vulnerabilities.
• User Consent: Apps should only use these APIs with explicit user consent.
• Manufacturer Restrictions: Some OEMs (e.g., Samsung, Xiaomi) may further restrict these APIs.