how is barcode scanner works

You've probably seen a barcode scanner "read" a barcode at work. We know that some form of intelligent understanding occurs when a flashing red light crosses a barcode. But what exactly happened?
The purpose of a barcode scanner is to scan or read a barcode symbol and then provide an electrical output to a computer through a decoder and cable. The decoder recognizes the type of barcode symbology it sees, translates the barcode and space content, and transmits the data to the computer in a human-readable format.
You don't need special software to retrieve barcode information. Just like how the human brain works and how we understand a number, letter, or picture, a decoder puts the barcode into a usable context. Many times it can be as simple as putting the data into an Excel or Access database. For more complex requirements, you may need special application software to put this data into inventory records, send and receive documents, or monitor work in process. If you want to print barcodes from downloaded data, you will also need special printing software to convert the human-readable content back into barcodes.
Twenty-odd years ago, you probably had a barcode scanner that could only read two or three types of barcodes. If you want to read a particular barcode, you're going to have to go out and find another type of scanner. Fortunately, as technology improved and more and more barcodes were created, barcode scanners were developed to read a wider variety of barcodes in 1D and 2D formats and then "automatically recognize" (in other words Saying, automatically determined) what symbology it reads and then correctly interprets the content.
In most cases, the decoder is built directly into the handle of the scanner. If not, there are a few other ways to decode and transmit barcodes: 

• Place a keyboard wedge between the scanner and the computer. A scanner is known as a wired or fixed-install scanner because it relies on a direct connection to the keyboard and computer via the Synapse cable. Once the barcode is scanned, the information is instantly transferred to the computer, just as if it were entered on a keyboard.
• Another type of fixed scanner transmits data through an RS-232 serial port on a computer. In this case, the serial scanner transmits the barcode in an ASCII file format, much like a wedge, which looks like keyed data. Both types of wired scanners come with handheld or hands-free options.
• To improve mobility, a portable batch scanner, the "Portable Data Terminal" (PDT), was developed. They store data to be sent to a computer at some point in the future. This device reads barcodes and you can see the information on an LCD. You can then enter additional data, such as inventory counts, via the keypad. PDT requires a "cradle" to hold the scanner and upload the scanned and entered data to the computer.
• For increased mobility and faster data retrieval, wireless portable scanners use a centrally located terminal, such as a cradle, to instantly transfer data to a computer when a barcode is scanned.