ESP32: Send Messages to WhatsApp

In this guide, you’ll learn how to send messages to your WhatsApp account with the ESP32. This can be useful to receive notifications from the ESP32 with sensor readings, alert messages when a sensor reading is above or below a certain threshold, when motion is detected, and many other applications. We’ll program the ESP32 using Arduino IDE and to send the messages we’ll use a free API called CallMeBot.

ESP32 Send Messages to WhatsApp Arduino IDE

We have a similar tutorial for the ESP8266 board:

Introducing WhatsApp

WhatsApp logo

“WhatsApp Messenger, or simply WhatsApp, is an internationally available American freeware, cross-platform centralized instant messaging and voice-over-IP service owned by Meta Platforms.” It allows you to send messages using your phone’s internet connection, so you can avoid SMS fees.

WhatsApp is free and is available for Android and iOS. Install WhatsApp on your smartphone if you don’t have it already.

CallMeBot WhatsApp API

To send messages to your WhatsApp account with the ESP32, we’ll use a free API service called CallMeBot service. You can learn more about CallMeBot at the following link:

Basically, it works as a gateway that allows you to send a message to yourself. This can be useful to send alert messages from the ESP32.

All the information about how to send messages using the API, can be found here.

Getting the CallMeBot API KEY

Before starting using the API, you need to get the CallmeBot WhatsApp API key. Follow the next instructions (check this link for the instructions on the official website).

  1. Add the phone number +34 644 31 95 65 to your Phone Contacts. (Name it as you wish);
  2. Send the following message: “I allow callmebot to send me messages” to the new Contact created (using WhatsApp of course);
  3. Wait until you receive the message “API Activated for your phone number. Your APIKEY is XXXXXX” from the bot.
Get CallMeBot API key

Note: If you don’t receive the API key in 2 minutes, please try again after 24hs. The WhatsApp message from the bot will contain the API key needed to send messages using the API

CallMeBot API

To send a message using the CallMeBot API you need to make a POST request to the following URL (but using your information):

https://api.callmebot.com/whatsapp.php?phone=[phone_number]&text=[message]&apikey=[your_apikey]
  • [phone_number]: phone number associated with your WhatsApp account in international format;
  • [message]: the message to be sent, should be URL encoded.
  • [your_apikey]: the API key you received during the activation process in the previous section.

For the official documentation, you can check the following link: https://www.callmebot.com/blog/free-api-whatsapp-messages/

Installing the URLEncode Library

As we’ve seen previously, the message to be sent needs to be URL encoded. URL encoding converts characters into a format that can be transmitted over the Internet. URLs can only be sent over the Internet using the ASCII character-set.

This will allow us to include characters like ç, ª, º, à, ü in our messages. You can learn more about URL encoding here.

You can encode the message yourself, or you can use a library, which is much simpler. We’ll use the UrlEncode library that can be installed on your Arduino IDE.

Go to Sketch > Include Library > Manage Libraries and search for URLEncode library by Masayuki Sugahara as shown below.

Install URL Encode Library Arduino IDE

Sending Messages to WhatsApp – ESP32 Code

The following example code sends a message to your WhatsApp account when the ESP32 first boots. This is a simple example to show you how to send messages. After understanding how it works, the idea is to incorporate it into your own projects.

/* 
  Rui Santos
  Complete project details at https://RandomNerdTutorials.com/esp32-send-messages-whatsapp/
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files.
  
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
*/

#include <WiFi.h>    
#include <HTTPClient.h>
#include <UrlEncode.h>

const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";

// +international_country_code + phone number
// Portugal +351, example: +351912345678
String phoneNumber = "REPLACE_WITH_YOUR_PHONE_NUMBER";
String apiKey = "REPLACE_WITH_API_KEY";

void sendMessage(String message){

  // Data to send with HTTP POST
  String url = "https://api.callmebot.com/whatsapp.php?phone=" + phoneNumber + "&apikey=" + apiKey + "&text=" + urlEncode(message);    
  HTTPClient http;
  http.begin(url);

  // Specify content-type header
  http.addHeader("Content-Type", "application/x-www-form-urlencoded");
  
  // Send HTTP POST request
  int httpResponseCode = http.POST(url);
  if (httpResponseCode == 200){
    Serial.print("Message sent successfully");
  }
  else{
    Serial.println("Error sending the message");
    Serial.print("HTTP response code: ");
    Serial.println(httpResponseCode);
  }

  // Free resources
  http.end();
}

void setup() {
  Serial.begin(115200);

  WiFi.begin(ssid, password);
  Serial.println("Connecting");
  while(WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to WiFi network with IP Address: ");
  Serial.println(WiFi.localIP());

  // Send Message to WhatsAPP
  sendMessage("Hello from ESP32!");
}

void loop() {
  
}

View raw code

How the Code Works

Sending a message to WhatsApp using the CallMeBot API is very straightforward. You just need to make an HTTP POST request.

First, include the necessary libraries:

#include <WiFi.h>    
#include <HTTPClient.h>
#include <UrlEncode.h>

Insert your network credentials on the following variables:

const char* ssid = "REPLACE_WITH_YOUR_SSID";
const char* password = "REPLACE_WITH_YOUR_PASSWORD";

Insert your phone number and API key. The phone number should be in international format (including the + sign).

String phoneNumber = "REPLACE_WITH_YOUR_PHONE_NUMBER";
String apiKey = "REPLACE_WITH_YOUR_API_KEY";

sendMessage()

We create a function called sendMessage() that you can call later to send messages to WhatsApp. This function accepts as an argument the message you want to send.

void sendMessage(String message){

Inside the function, we prepare the URL for the request with your information, phone number, API key, and message.

As we’ve seen previously, the message needs to be URL encoded. We’ve included the UrlEncode library to do that. It contains a function called urlEncode() that encodes whatever message we pass as argument (urlEncode(message)).

String url = "https://api.callmebot.com/whatsapp.php?phone=" + phoneNumber + "&apikey=" + apiKey + "&text=" + urlEncode(message);

Create and start an HTTPClient on that URL:

HTTPClient http;
http.begin(url);

Specify the content type:

// Specify content-type header
http.addHeader("Content-Type", "application/x-www-form-urlencoded");

Finally, send the HTTP post request. The following line sends the request and saves the response code:

int httpResponseCode = http.POST(url);

If the response code is 200, it means the post request was successful. Otherwise, something went wrong.

// Send HTTP POST request
int httpResponseCode = http.POST(url);
if (httpResponseCode == 200){
  Serial.print("Message sent successfully");
}
else{
  Serial.println("Error sending the message");
  Serial.print("HTTP response code: ");
  Serial.println(httpResponseCode);
}

Finally, free up the resources:

// Free resources
http.end();

setup()

In the setup(), initialize the Serial Monitor for debugging purposes.

Serial.begin(115200);

Connect to your local network and print the board IP address.

WiFi.begin(ssid, password);
Serial.println("Connecting");
while(WiFi.status() != WL_CONNECTED) {
  delay(500);
  Serial.print(".");
}
Serial.println("");
Serial.print("Connected to WiFi network with IP Address: ");
Serial.println(WiFi.localIP());

Then, we can send a message to WhatsApp by simply calling the sendMessage() function. In this case, we’re sending the message Hello from ESP32!

// Send Message to WhatsAPP
sendMessage("Hello from ESP32!");

Demonstration

After inserting your network credentials, phone number and API key, you can upload the code to your board.

After uploading, open the Serial Monitor at a baud rate of 115200 and press the board RST button. It should successfully connect to your network and send the message to WhatsApp.

ESP Send Message to WhatsApp Serial Monitor

Go to your WhatsApp account. After a few seconds, you should receive the ESP32 message.

WhatsApp Receive Message from ESP32

Wrapping Up

In this tutorial, you learned how to use the CallMeBot API with the ESP32 to send messages to your WhatsApp account. This can be useful to send sensor readings regularly to your inbox, send a notification when motion is detected, send an alert message when a sensor reading is above or below a certain threshold, and many other applications.

We also have tutorials for other types of messages (email and Telegram messages):

We hope you find this tutorial useful.

Learn more about the ESP32 with our resources:

Thanks for reading.



Build Web Server projects with the ESP32 and ESP8266 boards to control outputs and monitor sensors remotely. Learn HTML, CSS, JavaScript and client-server communication protocols DOWNLOAD »

Build Web Server projects with the ESP32 and ESP8266 boards to control outputs and monitor sensors remotely. Learn HTML, CSS, JavaScript and client-server communication protocols DOWNLOAD »


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29 thoughts on “ESP32: Send Messages to WhatsApp”

  1. Would be possible to use a ESP8266 instead? I have multiple of those laying around the house and it would be a good project to try. Would you say an ESP32 is a more flexible platform than the 8266? I am very familiar with the later but never used the esp32.

    Reply
  2. Hello
    Again, a wonderful tutorial.
    I use Callmebot with iobroker to tell me when the washing machine is ready.
    But I found out that Callmebot is not free.
    I’m still happy to pay the 40ct per month and support the maker to provide us with such a platform. To try it out you can use it for free, after a few days you will get a request from Callmebot asking for support.
    Greetings Infoschwab

    Reply
  3. Exactly what I needed. Thanks. Slight error in code, constant character declarations need semi colons. OK in code explanation, but raw code and initial presentation, semi colons are missing.

    Reply
  4. Great project as usually Sara.
    We are waiting for a simple example on how to manage an alert messages when a sensor reading is above or below a certain threshold.
    Thanks.

    Reply
  5. Excellent tutorial as always, thank for that.
    My concern is about privacy, providing that your message is being sent to a third party site that forwards it to you. With the information that you load in the site, can’t this third party send other undesired messages to you? I’m not saying that they’re going to do, but if they’re hacked…. Telegram APIs don’t need a third party site, I think.

    Reply
  6. Having problems finding the right library for #include <HTTPClient.h>
    I found #include <HttpClient.h> from HttpClient-2.2.0.zip, but camel-case is very different from what you used. Could you send me a link to the right one?

    Reply
  7. Thank you for bringing this to our attention! I’m not sure if this will remain a possibility for long, but for now I’ll make use of it! thanks again. Regards.

    Reply
  8. hello,
    thanks for demo.. i can now send text .. but how to send a VARIABLE ? .. like my sensor reading is 23.7 next minute it is 23.9 or so .. so how to send variables instead of “message”
    that variable temperature is stored in int. named Ctemp so if i sent “Ctemp” it is sent as a text named Ctemp not its integer value… can you help please?
    – just what would be the syntax for that?

    Reply
  9. Thanks for the excellent tutorials, all very helpful.
    I’m usina ESP32 board and Arduino IDE. I followed the steps on the tutorial but when I run the sketch always receive this message on serialmonitor: “Error sentindo the message. HTTP responde code: 403. Do you know how to fix it? Thanks a lot.

    Reply
  10. Hi !!!! greetings from Argentina. Done the project with ESP32 , sound sensor and pir sensor, works incredibly !!
    I read a comment from a user that in few days callmebot stops being free, is it true ?
    Is it possible to use both ways, I mean, receive a message from an event, and send a whatsapp message to ESP32 so it turns HIGH or LOW a given port.
    Thanks for everything !!!!!!!!!!

    Reply
    • Hi.
      Yes, you need internet connection so that ESP32 can connect with the callmebot API that will take care of sending the message.
      Regards,
      Sara

      Reply
  11. Hallo, super Beitrag wie immer – auf Ihre Beiträge kann man sich verlassen, vor allen Dingen wenn man nicht ganz so firm ist mit der Programmierung.
    Nun zu meiner Frage: Haben Sie schon eine Variante um z.B. das Signal eines Bewegungsmelders an WhatsApp zu senden ?
    Unbedingt veröffentlichen wenn es soweit ist…..

    Vielen Dank
    XXAL

    Reply

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