A barcode reader is a data acquisition device that can read and pass on various barcodes. The recognition of these barcodes is purely optical, using either red or infrared light. Each barcode reader consists of the actual reading unit and a downstream decoding unit. While the reading pens usually contain two devices (there are also reading pens with an integrated decoder), the decoding unit is integrated in the reading unit in almost all other device types. Almost all types are now available on the market as stationary, wired hand-held scanners or mobile recording devices (e.g. inventory terminals with integrated barcode scanners).