Recently I had an unpleasant experience in my home, specifically my ground floor was flooded as a result of a burst water pipe, and at that moment I was absent. So I decided to develop a warning system for such phenomena that would also take some action in order to prevent greater damage from occurring. For this purpose, I purchased the Gravity: Photoelectric High Accuracy Liquid Level Sensor for Arduino from DFRobot which has good sensitivity and no need for mechanical parts and is also corrosion resistant and can handle high temperature and high pressure. 

   The way this photoelectric sensor works is as follows:
 - When the detected level is in air, due to reflect of the prism, most of light will enter receiver LED, optical level sensor will output high voltage.

 - When the detected level is in water, due to refraction of the liquid, just less of light enter receiver LED, optical level sensor will output low voltage.

The level of the output voltage from this sensor is the same as the power supply, and since it can be powered by 3V3, I can connect it directly to the ESP32 Input. It can be mechanically installed in any direction, and specifically for this demonstration I made a small stand on which the sensor is mounted. The tip of the sensor should be just above the floor to detect even the slightest accumulation of water. As I mentioned earlier, I plan to use an ESP32 microcontroller for several reasons. It is cheap, has low power consumption, supports Wi-Fi and Bluetooth, and has other advantages over most Arduino boards.

A basic requirement when planning my project was the option to receive information about the current situation no matter where I am, via the mobile network on my smartphone. There are several services for this purpose, and I chose the Telegram platform because it allows the creation of bots that can perform automated tasks, and completely free of charge, so because of these conveniences it is often called a programmer's paradise. 

 This project is sponsored by PCBWay. From July 1st to July 31st, 2026, PCBWay is organizing 12th anniversary campaig. Grab your discount and unlock more rewards in the form of Exclusive Coupons, PCB Order for Just $5, Turnkey Electronic Design Services, Up to 50% off for 3D printing & CNC Machining, and Special Sales in PCBWay Store. Next, Join the fun with interactive games and receive your exclusive Engineer Color Personality, Click the Box to Participate in the Lucky Draw, Show Your Colorful Projects, and Vote for the Most Popular Badge.
   So, if you haven't had one before, you need to open a Telegram account and create a bot. 
  Step-by-Step Guide: How to Create a Telegram Bot and Get Your Chat ID

Part 1: Creating the Telegram Bot

1. Download and install Telegram if you haven’t already.
2. In the Telegram search bar, type @BotFather and select the official verified account.
3. Press the "Start" button to activate BotFather.
4. In the message box, type and send: `/newbot`
5. Enter a friendly name for your new bot (for example: `micemk_wateralarm_bot`).
6. Next, choose a unique Username for your bot. Note: It must end with `_bot` (for example: `Mircemk_bot`).
7. Once the username is accepted, BotFather will instantly generate an HTTP API Token. Make sure to copy and save this token securely, as you will need it for your ESP32 code.

Part 2: Obtaining Your Chat ID

1. In the Telegram search bar, search for your newly created bot username (e.g., @Mircemk_bot) and press "Start" to initialize it.
2. Go back to the Telegram search bar and search for a utility bot named: @IDBot
3. Open the chat with @IDBot and send the command: `/getid`
4. The bot will instantly reply with your unique, numeric Chat ID. Copy and save this number to use in your Arduino configuration.

    It is important that when creating a telegram bot we get two distinct unique strings of characters, one is the HTTP API Token, and the other is the ID. We...