Building Touchless Arduino Doorbell

The Building Touchless Arduino Doorbell system operates by integrating chemical detection with microcontroller logic to trigger an audible alert without requiring physical contact. At the core of the circuit is the MQ-3 Alcohol Sensor, which monitors the air for specific volatile organic compounds like alcohol vapors typically found in hand sanitizers. When a user brings their freshly sanitized hands close to the sensor, the MQ-3 detects the elevated vapor concentration and outputs a corresponding analog voltage signal to the Arduino Uno. The Arduino Uno processes this incoming analog signal, evaluating whether it crosses a predefined threshold programmed via the Arduino IDE. Upon confirming a valid detection event, the microcontroller sends a control signal to the IC-ULN2003 Darlington transistor array, which provides the necessary current amplification to switch the 5V Relay safely. The energized relay acts as an electrically operated switch that completes the higher-voltage circuit, allowing power from the 12V 2A adapter to activate the Electric Doorbell. Simultaneously, an LED paired with a 220 Ohm Resistor illuminates on the breadboard to provide a clear visual confirmation that the touchless trigger has been successfully registered by the system.