APP

 Reciever BackGroundListening.java

package com.assist;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.speech.RecognitionListener;
import android.speech.RecognizerIntent;
import android.speech.SpeechRecognizer;
import android.speech.tts.TextToSpeech;
import android.util.Log;

import java.util.ArrayList;
import java.util.Locale;

public class BackGroundListening extends BroadcastReceiver{


    private static final int REQUEST_CODE_SPEECH_INPUT = 1000;
    private TextToSpeech mTextToSpeech;
    SpeechRecognizer mSpeechRecognizer;
    Intent mSpeechRecognizerIntent;
    String FinalRecognizedText;

    @Override
    public void onReceive(Context context, Intent intent2) {

        mSpeechRecognizer = SpeechRecognizer.createSpeechRecognizer(context);

        mTextToSpeech = new TextToSpeech(context, new TextToSpeech.OnInitListener() {
            @Override
            public void onInit(int status) {
                if (status == TextToSpeech.SUCCESS)
                {
                    int result = mTextToSpeech.setLanguage(Locale.ENGLISH);

                    if(result == TextToSpeech.LANG_MISSING_DATA || result == TextToSpeech.LANG_NOT_SUPPORTED)
                    {
                        Log.e("TTS", "Language not Supported");
                    }
                }
                else
                {
                    Log.e("TTS", "INITIALIZATION FAILED");
                }
            }
        });

        while (true){
            mSpeechRecognizer.startListening(mSpeechRecognizerIntent);
            Listen();
        }
    }

    private void Speak(String speech){
        mTextToSpeech.speak(speech, TextToSpeech.QUEUE_FLUSH, null);
    }

    public void Listen(){

        mSpeechRecognizerIntent = new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH);
        mSpeechRecognizerIntent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL,RecognizerIntent.LANGUAGE_MODEL_FREE_FORM);
        mSpeechRecognizerIntent.putExtra(RecognizerIntent.EXTRA_LANGUAGE, Locale.getDefault());

        mSpeechRecognizer.setRecognitionListener(new RecognitionListener() {
            @Override
            public void onReadyForSpeech(Bundle params) {

            }

            @Override
            public void onBeginningOfSpeech() {

            }

            @Override
            public void onRmsChanged(float rmsdB) {

            }

            @Override
            public void onBufferReceived(byte[] buffer) {

            }

            @Override
            public void onEndOfSpeech() {

            }

            @Override
            public void onError(int error) {

            }

            @Override
            public void onResults(Bundle results) {
                ArrayList<String> recognizedText = results.getStringArrayList(SpeechRecognizer.RESULTS_RECOGNITION);

                if(recognizedText!=null){
                    FinalRecognizedText =  (recognizedText.get(0)).toLowerCase();

                    if(FinalRecognizedText.contains("hello"))
                    {
                        Speak("Hello sir");
                    }

                }
            }

            @Override
            public void onPartialResults(Bundle partialResults) {

            }

            @Override
            public void onEvent(int eventType, Bundle params) {

            }
        });
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.assist">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        
        <receiver android:name=".BackGroundListening"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="BackGroundListening"/>
            </intent-filter>
        </receiver>


    </application>

</manifest>

Main Activity

package com.assist;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.hardware.Camera;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.provider.Settings;
import android.speech.RecognitionListener;
import android.speech.RecognizerIntent;
import android.speech.SpeechRecognizer;
import android.speech.tts.TextToSpeech;
import android.telephony.SmsManager;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ToggleButton;

import com.chaquo.python.PyObject;
import com.chaquo.python.Python;
import com.chaquo.python.android.AndroidPlatform;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Locale;

import static android.widget.Toast.LENGTH_SHORT;

public class MainActivity extends AppCompatActivity {
    private static final int REQUEST_CODE_SPEECH_INPUT = 1000;
    private TextToSpeech mTextToSpeech;
    SpeechRecognizer mSpeechRcognizer;
    Intent mSpeechRecognizerIntent;
    String FinalRecognizedText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        checkPermission();

        Intent intent1 = new Intent(this, BackGroundListening.class);
        intent1.setAction("BackGroundListening");

        PendingIntent pendingIntent;
        pendingIntent = PendingIntent.getBroadcast(this, 0,intent1,0);

        AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);

        alarmManager.setRepeating(AlarmManager.RTC_WAKEUP,0,10,pendingIntent);

        finish();

    }
    private void  checkPermission() {
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)
        {
            if(!(ContextCompat.checkSelfPermission(this,Manifest.permission.RECORD_AUDIO) == PackageManager.PERMISSION_GRANTED))
            {
                Intent intent = new Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS, Uri.parse("package:"+ getPackageName()));
                startActivity(intent);
                finish();
            }
        }
    }


}