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A barcode reader, or scanner, is an input device that uses a light source to read the optical pattern of a barcode, decode the data it contains, and transmit that information to a computer. The data from the barcode is then typically used to look up related information in a database, such as a product's price, stock level, and description.

A typical barcode reader contains four basic components:

Light source: An LED or laser lights up the barcode to create the necessary contrast for the scanner to read the pattern.

Lens: A lens in the scanner captures the image of the barcode's black and white pattern.

Photoconductor: A light sensor, or photodiode, measures the light reflected back from the barcode's dark and light areas and converts it into an electrical signal.

Decoder: An internal circuit or external software interprets the electrical signal, validates it using the barcode's check digit, and converts it into data (e.g., numbers and letters).

Barcode scanners vary in their technology and form factor:

Pen-type readers:
Laser scanners:
CCD readers:
Imager readers:
Omnidirectional scanners: