Barcodes are read by sweeping a small spot of light across the printed barcode symbol. Your eyes only see a thin red line emitted from the laser scanner. But what's happening is that the scanner's light source is being absorbed by the dark bars and reflected by the light spaces. A device in the scanner takes the reflected light and converts it into an electrical signal.

The scanner's laser (light source) starts to read the barcode at a white space (the quiet zone) before the first bar and continues passing by the last bar, ending in the white space which follows it. Because a barcode cannot be read if the sweep wanders outside the symbol area, bar heights are chosen to make it easy to keep the sweep within the barcode area. The longer the information to be coded, the longer the barcode needed. And as the length increases, so does the height of the bars and spaces to be read.

There are three basic types of barcode scanners—fixed, portable batch, and portable wireless. Fixed scanners (hand held or mounted) remain attached to their host computer or terminal, and transmit one data item at a time as the barcode is scanned.

Portable batch scanners are battery operated and store data in memory for later batch transfer to a host computer. Wireless portable scanners also store data in memory, however data is transmitted to the host in real time. This allows for instant access to all data for management decisions.