Radio-frequency identification (RFID) is the use of an object (typically referred to as an RFID tag) applied to or incorporated into a product, animal, or person for the purpose of identification and tracking using radio waves. Some tags can be read from several meters away and beyond the line of sight of the reader.
Radio-frequency identification comprises interrogators (also known as readers), and tags (also known as labels).
Most RFID tags contain at least two parts. One is an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency (RF) signal, and other specialized functions. The second is an antenna for receiving and transmitting the signal.
There are generally three types of RFID tags: active RFID tags, which contain a battery and can transmit signals autonomously, passive RFID tags, which have no battery and require an external source to provoke signal transmission, and battery assisted passive (BAP) RFID tags, which require an external source to wake up but have significant higher forward link capability providing greater range.
There are a variety of groups defining standards and regulating the use of RFID, including: International Organization for Standardization (ISO), International Electrotechnical Commission (IEC), ASTM International, DASH7 Alliance, EPCglobal. (Refer to Regulation and standardization below.)
RFID has many applications; for example, it is used in enterprise supply chain management to improve the efficiency of inventory tracking and management

Bag tags, also known as baggage tags, baggage checks or luggage tickets, have traditionally been used by bus, train and airline companies to route passenger luggage that is checked on to the final destination. The passenger stub is typically handed to the passenger or attached to the ticket envelope: a) to aid the passenger in identifying their bag among similar bags at the destination baggage carousel; b) as proof—still requested at a few airports—that the passenger is not removing someone else's bag from the baggage reclaim hall; c) as a means for the passenger and carrier to identify and trace a specific bag that has gone astray and was not delivered at the destination.

Prior to the 1990s, airline bag tags consisted of a paper tag attached with a string.

The tag contained basic information:

Airline/carrier name
flight number
6 digit code; at one point it was 5 and later 10
name of airport of arrival
These tags became obsolete as they offered little security and easy to replicate.

Current bag tags include a bar code. These bag tags are printed using thermal or barcode printers that print on an adhesive paper stock. This printed strip is then attached to the luggage at check in. This allows for automated sorting of the bags to reduce the number of misrouted, misplaced or delayed bags. The limitations of this technology was apparent at Denver International Airport when a fully automated cart-based system significantly delayed the airport's opening. United Airlines announced in August 2005 that the cart-based system at Denver was to be scrapped. While the inability to reliably read all bar-coded tags in the Denver installation was a part of the problem, it was one of several technical reasons for the delayed opening. Nevertheless, automated sorting of baggage using laser scanner arrays, known as automatic tag readers, to read bar-coded bag tags is standard at major airports.

For flights within the European Union, bag tags are issued with green edges. Passengers are eligible to take these bags through a separate "Blue Channel" at Customs.

Bar codes can not be automatically scanned without direct sight and undamaged print. Forced by reading problems with poorly-printed, obscured, crumpled, scored or otherwise damaged bar codes, some airlines have started using radio-frequency identification (RFID) chips embedded in the tags. In the US, McCarran International Airport has installed an RFID system throughout the airport. Hong Kong International Airport has also installed an RFID system. The International Air Transport Association (IATA) is trying to standardize RFID bag tags. There is a somewhat higher probability of reading RFID tags automatically. Physically, however, RFID tags are not more robust than barcode tags.

A symbology is equivalent to a language. Each symbology has its strengths and weaknesses. Some symbologies have restrictions on the type and/or amount of data they can encode into a bar code.
The following is a list of some of the most common symbologies:
• UPC-A
UPC (Universal Product Code) is the standard code for items for sale to the public. This is the code that is seen on items in the supermarket. UPC-A encodes 12 numeric digits, the twelfth being a check digit.
• UPC-E
Also known as the "zero suppression version UPC", the UPC-E is used in the retail industry for smaller packages where the UPC-A would not fit. The data must contain 7 numeric digits with the software calculating the 8th, which is a check digit.
• EAN 8
Used in the international retail industry. The data must contain 7 numeric digits. The software will determine the 8th digit.
• EAN 13
Also used in the international retail industry. The data must contain 12 numeric digits. The program will calculate the 13th digit, which is a check digit.
• Code 39
This code is also the most popular symbology in the non-retail world and is used extensively in manufacturing, distribution, military, and health applications. It can be read by almost any bar code reader. Alpha-numeric.
• Code 128
Used by many industries for inventory control. Data is of variable length and can be alpha-numeric. Code 128 is more condensed than Code 39, and therefore preferred when longer information needs to be coded.
• UCC/EAN 128 / Multi
This is a specialized application of the Code 128 symbology which requires data to be numeric only. The exact specifications of what each piece of the data means varies between industries. The Multi option requires more exacting input; but as a result allows data entry functions to be automated.
• Interleaved 2 Of 5
Used in many types of industry, the data can be of any length but must contain an even number of characters, otherwise the printer will add a leading zero. It accepts only numeric values.

Codabar
Used primarily in the library and medical industries, this symbology allows data of variable length and can contain both numbers and characters.

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