How do barcodes work?

The scanner shines red light across the code; the dark bars absorb it while the white spaces reflect it back to a sensor. The sensor turns the pattern of reflections into an electrical signal of on and off pulses, which is decoded into digits. A standard UPC-A barcode holds 12 digits, and the last one is a check digit that catches reading errors. The barcode itself does not contain the price: the till looks the number up in the shop’s database. The idea was patented in 1952 by Norman Joseph Woodland and Bernard Silver, and the first product scanned in a shop was a pack of Wrigley’s gum in Troy, Ohio, on 26 June 1974.