Phone Authentication in Android with Firebase: Complete Tutorial (2026) | D.Tech Academic

Phone Authentication in Android with Firebase: Complete Tutorial (2026)

Last Updated: October 2026 | Author: Deep Singh

Phone number authentication is one of the most convenient login methods for mobile apps. Users type their phone number, receive an SMS with a one-time password (OTP), enter it, and they're logged in — no password to remember, no email verification loop.

In this tutorial, you'll implement Firebase Phone Authentication in Android from scratch. We'll walk through creating a Firebase project, enabling phone sign-in, wiring up the Gradle dependencies, and building a working login screen with OTP verification.

Output Screens

The final app has a login screen with a mobile number input and an OTP input field, plus a home page that shows the signed-in user and a logout button.

Creating a Firebase Project

Open the Firebase Console and sign in with your Google account. Click Add Project, give it a name (e.g., Phone Authentication), and follow the wizard.

Once the project is created, register your Android app by entering the package name from your AndroidManifest.xml. Download the generated google-services.json file — you'll need to place it in your project shortly.

Enabling Phone Authentication

In the Firebase Console, navigate to Authentication → Sign-in method. Enable the Phone sign-in provider. If you want, you can also enable Email/Password or other providers at the same time.

Important: Firebase requires your app's SHA-1 fingerprint to enable phone authentication. You can get it by running ./gradlew signingReport in Android Studio's Terminal, then copy the SHA-1 value into your Firebase project settings.

Configuring Android Studio

In your app-level build.gradle, add the Firebase Auth dependency:

dependencies {
    // Use the Firebase BoM so all Firebase libraries align
    implementation platform('com.google.firebase:firebase-bom:33.5.1')
    implementation 'com.google.firebase:firebase-auth'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
}

And apply the Google Services plugin at the bottom of the file:

apply plugin: 'com.google.gms.google-services'

Also make sure your project-level build.gradle includes the Google Services classpath:

buildscript {
    dependencies {
        classpath 'com.google.gms:google-services:4.4.2'
    }
}

Place google-services.json inside app/ in your project, and sync Gradle.

Note on versions: The original tutorial used firebase-auth:16.0.5. That version is several years old and doesn't work with modern Flutter or Firebase BoM setups. Use the BoM approach shown above.

Layouts

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop"
        android:src="@drawable/back_document" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@id/ll"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="70dp"
        android:text="Phone Authentication"
        android:textColor="#fff"
        android:textSize="30sp"
        android:textStyle="bold"
        android:typeface="serif" />

    <LinearLayout
        android:id="@+id/ll"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:orientation="vertical">

        <EditText
            android:id="@+id/mymobile"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="20dp"
            android:layout_marginRight="20dp"
            android:background="@drawable/button"
            android:hint="Enter Mobile Number"
            android:inputType="number"
            android:maxLength="10"
            android:padding="20dp"
            android:textColor="#fff"
            android:textColorHint="#fff" />

        <EditText
            android:id="@+id/myotp"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="20dp"
            android:layout_marginRight="20dp"
            android:background="@drawable/button"
            android:hint="OTP Number"
            android:inputType="number"
            android:maxLength="6"
            android:padding="20dp"
            android:textColor="#fff"
            android:textColorHint="#fff" />

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="50dp"
            android:layout_marginRight="20dp"
            android:background="@drawable/button"
            android:onClick="generate"
            android:text="Generate"
            android:textAllCaps="false"
            android:textColor="#fff"
            android:textStyle="bold"
            android:typeface="serif" />

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:layout_marginTop="20dp"
            android:layout_marginRight="20dp"
            android:background="@drawable/button"
            android:onClick="verify"
            android:text="Verify & Login"
            android:textAllCaps="false"
            android:textColor="#fff"
            android:textStyle="bold"
            android:typeface="serif" />

    </LinearLayout>

</RelativeLayout>

activity_home_page.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop"
        android:src="@drawable/back_document" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:padding="20dp"
        android:text="Welcome To Home Page"
        android:textColor="#fff"
        android:textSize="20sp"
        android:textStyle="italic"
        android:typeface="serif" />

    <TextView
        android:id="@+id/mytext"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerInParent="true"
        android:padding="20dp"
        android:textColor="#fff"
        android:textSize="20sp"
        android:typeface="serif" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginLeft="20dp"
        android:layout_marginRight="20dp"
        android:layout_marginBottom="20dp"
        android:background="@drawable/button"
        android:onClick="logout"
        android:text="Logout"
        android:textColor="#fff"
        android:textStyle="bold" />

</RelativeLayout>

drawable/button.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <stroke
        android:width="1dp"
        android:color="#fff" />
    <corners
        android:bottomRightRadius="10dp"
        android:topLeftRadius="10dp" />
</shape>

MainActivity.java

package com.example.phoneauthentication;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.FirebaseException;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.PhoneAuthCredential;
import com.google.firebase.auth.PhoneAuthProvider;

import java.util.concurrent.TimeUnit;

public class MainActivity extends AppCompatActivity {

    private EditText tmobile, totp;
    private PhoneAuthProvider.OnVerificationStateChangedCallbacks myCallbacks;
    private FirebaseAuth mAuth;
    private String verificationCode;

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

        tmobile = findViewById(R.id.mymobile);
        totp = findViewById(R.id.myotp);
        firebaseLogin();
    }

    /**
     * Called by the "Generate" button. Sends an OTP to the entered
     * phone number.
     */
    public void generate(View view) {
        String phone = tmobile.getText().toString().trim();
        if (phone.isEmpty() || phone.length() < 10) {
            Toast.makeText(this, "Enter a valid 10-digit mobile number", Toast.LENGTH_SHORT).show();
            return;
        }

        PhoneAuthProvider.getInstance().verifyPhoneNumber(
                "+91" + phone,          // Phone number with country code
                60,                     // Timeout duration
                TimeUnit.SECONDS,       // Timeout unit
                this,                   // Activity for callback
                myCallbacks             // Callback handler
        );
    }

    /**
     * Called by the "Verify & Login" button. Verifies the code entered
     * by the user against the code Firebase sent via SMS.
     */
    public void verify(View view) {
        String otp = totp.getText().toString().trim();
        if (otp.isEmpty()) {
            Toast.makeText(this, "Enter the OTP", Toast.LENGTH_SHORT).show();
            return;
        }

        PhoneAuthCredential credential =
                PhoneAuthProvider.getCredential(verificationCode, otp);
        signInWithPhone(credential);
    }

    private void firebaseLogin() {
        mAuth = FirebaseAuth.getInstance();
        myCallbacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {

            @Override
            public void onVerificationCompleted(@NonNull PhoneAuthCredential credential) {
                // Auto-retrieval succeeded — sign in directly
                Log.d("PhoneAuth", "Auto-verification succeeded");
                totp.setText(credential.getSmsCode());
                signInWithPhone(credential);
            }

            @Override
            public void onVerificationFailed(@NonNull FirebaseException e) {
                Log.e("PhoneAuth", "Verification failed", e);
                Toast.makeText(MainActivity.this,
                        "Verification failed: " + e.getMessage(),
                        Toast.LENGTH_LONG).show();
            }

            @Override
            public void onCodeSent(@NonNull String s,
                                   @NonNull PhoneAuthProvider.ForceResendingToken token) {
                super.onCodeSent(s, token);
                verificationCode = s;
                Log.d("PhoneAuth", "OTP sent. verificationId = " + s);
                Toast.makeText(MainActivity.this,
                        "OTP sent to your phone",
                        Toast.LENGTH_SHORT).show();
            }
        };
    }

    private void signInWithPhone(PhoneAuthCredential credential) {
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            Toast.makeText(MainActivity.this,
                                    "Signed in successfully",
                                    Toast.LENGTH_SHORT).show();
                            goToHomePage();
                        } else {
                            Toast.makeText(MainActivity.this,
                                    "Sign-in failed: " + task.getException(),
                                    Toast.LENGTH_LONG).show();
                        }
                    }
                });
    }

    @Override
    protected void onStart() {
        super.onStart();
        FirebaseUser user = mAuth.getCurrentUser();
        if (user != null) {
            goToHomePage();
        }
    }

    private void goToHomePage() {
        startActivity(new Intent(MainActivity.this, HomePage.class));
        finish();
    }
}

HomePage.java

package com.example.phoneauthentication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class HomePage extends AppCompatActivity {

    private FirebaseAuth mAuth;

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

        mAuth = FirebaseAuth.getInstance();

        TextView ttext = findViewById(R.id.mytext);
        FirebaseUser user = mAuth.getCurrentUser();
        if (user != null) {
            String displayName = user.getDisplayName() != null
                    ? user.getDisplayName()
                    : "User";
            String email = user.getEmail() != null
                    ? user.getEmail()
                    : "No email";
            String phone = user.getPhoneNumber() != null
                    ? user.getPhoneNumber()
                    : "No phone";
            ttext.setText(displayName + "\n" + email + "\n" + phone);
        }
    }

    public void logout(View view) {
        mAuth.signOut();
        startActivity(new Intent(this, MainActivity.class));
        finish();
    }
}

AndroidManifest.xml

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

    <uses-permission android:name="android.permission.INTERNET" />

    <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=".HomePage" />
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

</manifest>

Common Pitfalls

Missing SHA-1 fingerprint. Without it, Firebase will refuse to send an OTP. Register both your debug and release SHA-1 in the Firebase Console.
Test numbers during development. Firebase lets you add test phone numbers and codes in the Console → Authentication → Sign-in method → Phone → Phone numbers for testing. Use them to avoid hitting SMS quotas.
Wrong phone number format. Firebase needs the country code (e.g., +91 for India). If you forget it, verification will fail silently.
Auto-retrieval can fire on emulators. The onVerificationCompleted callback may fire before you've entered anything, so it's safe to also fill the OTP field automatically (as shown).
Expired verification IDs. The verificationId returned in onCodeSent is only valid for a limited time (typically the timeout you set). If you wait too long, verification fails.
Using old Firebase SDKs. The firebase-auth:16.0.5 version from 2018 tutorials is not compatible with current Android Gradle Plugin versions. Use the Firebase BoM approach.
Forgetting to call Firebase.initializeApp(). The plugin auto-initialises from google-services.json, but if you've moved to a manual setup, you must call it explicitly in your Application class.
Not handling the onStart auto-login check. If a user is already signed in, they should skip the login screen. The example does this in onStart.

Wrapping Up

You now have a working Firebase Phone Authentication flow in Android. Users enter their phone number, Firebase sends an OTP, they verify it, and they're logged in. The HomePage shows the signed-in user and includes a logout button.

From here, you can extend the app with:

Resend OTP. Use the ForceResendingToken from onCodeSent to allow resending without a full restart.
Multiple auth providers. Combine phone auth with Google Sign-In or email/password for a complete authentication system.
Firestore integration. Store user profile data linked to the Firebase UID after sign-in.
Modern UI. Replace the plain EditText/Button layout with Material 3 components or Jetpack Compose for a cleaner look.
Test phone numbers. Add fake numbers in the Firebase Console so you can test freely without burning SMS quota.

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Phone Authentication using Android with Firebase