package io.akessler.elixircounter;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Intent overlayService = new Intent(this, OverlayService.class);
        startService(overlayService);
        finish();
    }
}

package io.akessler.elixircounter;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    /* Used to handle permission request */
    private static final int PERMISSIONS_REQUEST_RECORD_AUDIO = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Check if user has given permission to record audio
        int permissionCheck = ContextCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.RECORD_AUDIO);
        if (permissionCheck != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.RECORD_AUDIO}, PERMISSIONS_REQUEST_RECORD_AUDIO);
            return;
        }

        startOverlayService();
    }

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);

        if (requestCode == PERMISSIONS_REQUEST_RECORD_AUDIO) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                startOverlayService();
            } else {
                finish();
            }
        }
    }

    private void startOverlayService() {
        Intent overlayService = new Intent(this, OverlayService.class);
        startService(overlayService);
        finish();
    }
}

Add permissions check to allow recording audio with mic