Barcode scanners are devices which use some sort of light-emitting device and a photo conductor to read barcodes. They are usually designed to attach to a computer, via either PS2 or some other interface, though they may also be used on their own and store the data for future retrieval by a computer.
Barcodes are simple visual representations of data which can be transferred to a computer via a barcode scanner. Traditional barcodes consist of parallel lines, but a number of variations now exist, including scatterings of dots and embedded codes hidden within images. Barcodes were first conceived in the late 1940s and became widely implemented starting in the early 1970s. The first product sold with a barcode was a pack of Wrigley's Juicy Fruit gum, at Marsh's supermarket in Ohio, one of the first stores to implement barcode scanners. The gum now belongs to the Smithsonian and symbolizes a key moment in US history.
Barcode scanners typically utilize a laser scanner, though LED and imaging varieties also exist. Light is shot out of the barcode scanner onto the barcode, then reflected back, picked up by a photodiode in the scanner and decoded. The decoded information is then transmitted to the computer that the scanner is hooked up to.
Barcode scanners may be completely handheld, in which case they usually look almost like a science-fiction era gun, with a laser emitting from the barrel, and a trigger to turn the light on or off. These are found in some stores, and consumer-level barcode scanners are most often of this variety. Barcode scanners may also be built into a surface such as a register counter, so that barcodes can be read by swiping them across the laser. These types of barcode scanners are most typically found in supermarkets because of their ease of use and speed.
Smaller barcode scanners, often shaped like small pens, are also in use. This variety is often found in video stores or book stores. Their smaller, usually lower-quality light source does not allow for the same consistency of reading as larger scanners, but is often adequate for simple uses.
A number of barcode standards are in use today, including Code 128, Code 39, and the Universal Product Code (UPC). Most barcode scanners on the market are capable of reading and decoding all of the major barcode standards.
Barcode scanners may also be used on a consumer level to track one's own purchasing habits. Consumer barcode scanners are usually of the handheld variety, easily swept over all purchases. They store the data locally, later to be uploaded to a computer at the user's convenience.