This project is a fire detection system that continuously monitors ambient temperature using a DHT11 sensor connected to an ESP8266 microcontroller. When the sensor reading exceeds a set temperature (50 °C for example), a buzzer is activated and an SMS alert is sent via a SIM800L GSM module to a predefined phone number. This device provides immediate local warning and remote notification, helping to prevent fire-related incidents in homes or workspaces.

The system consists of both hardware and software modules working together:

• ESP8266 Microcontroller: Reads temperature data, processes the threshold logic, controls the buzzer, and interfaces with the GSM module.
• DHT11 Temperature Sensor: Provides real-time temperature readings to the microcontroller over a digital signal.
• Buzzer: Emits an audible alarm when the temperature crosses a set value.
• SIM800L GSM Module: Sends SMS alerts over UART to notify remote users.
• Push button: Stops the buzzer alarm.

- Temperature Sensor DHT11

• Data (OUT) → pin D2 (GPIO4) of the ESP8266 board
• VCC → 3.3V
• GND → GND

- Button (Reset Alarm)

• First pin → pin D1 (GPIO5) of the ESP8266
• Second pin → 3.3V
• Third pin → GND
• Software configuration: internal pull-up resistor is enabled with pinMode(D1, INPUT_PULLUP);
• Purpose: Temporarily stops the alarm and resets the alert state.

- Passive Buzzer

• Signal pin → pin D0 (GPIO16)
• GND → GND
• Purpose: Emits a warning sound when the temperature exceeds the threshold. Controlled with tone() and noTone().

- SIM800L GSM Module

• TX (SIM800L output) → pin D7 (ESP8266 RX)
• RX (SIM800L input) → pin D8 (ESP8266 TX)
• Note: A voltage divider is recommended on ESP8266 TX → SIM800L RX, as the ESP outputs 3.3V and the SIM800L is sensitive.
• VCC → separate 3.7V power source (Li-ion battery) or stabilized step-down converter
• GND → Common GND with ESP8266
• Purpose: Sends a warning SMS only once for each alarm trigger.

- ESP8266 (NodeMCU)

• USB → PC (for power and serial communication)
• Purpose: Acts as the system's control unit. It receives data from the sensor, decides whether to activate the alarm, and communicates via GSM.

The firmware is developed in the Arduino IDE targeting the ESP8266 platform. It follows these steps:

1. Initialize the DHT11 sensor, buzzer pin, and UART communication with the SIM800L.
2. Enter a loop where temperature is read every two seconds.
3. If the temperature reading exceeds 50 °C, activate the buzzer and transmit an SMS alert via the GSM module using standard AT commands.
4. Otherwise, keep the buzzer silent and continue monitoring.