A barcode scanner (or barcode reader) is a data capture device that instantly reads and interprets the information stored in a visual barcode pattern, converting it into a usable digital format. The device operates on three key principles: illumination, light detection, and decoding. It begins by projecting a light source (often a laser or LED) onto the barcode symbol. The dark bars on the code absorb the light, while the light spaces reflect it brightly back to the scanner's internal sensor. This sensor then converts the varying intensity of the reflected light into an analog electrical signal. This signal is sent to an internal decoder, which uses a specialized algorithm to analyze the widths and sequence of the bars and spaces. The decoder interprets this pattern based on known barcode standards (like UPC or Code 128), validates the information, and translates it into the final alphanumeric data (e.g., a product number). The resulting data is then transmitted to a host system (like a POS terminal or inventory software), effectively replacing slow and error-prone manual data entry, making it indispensable for efficient business operations.