use they have a number of important advantages over the older bar- code technology. RFID codes are long enough that every RFID tag may have a unique code, whereas UPC codes are limited to a single code for all instances of a particular product. The uniqueness of RFID tags means that a product may be indi- vidually tracked as it moves from location to location, finally ending up in the con- sumer's hands. This may help to combat theft and other forms of product loss. It has also been proposed to use RFID for point-of-sale store checkout to replace the cashier with an automatic system, with the option of erasing all RFID tags at checkout and paying by credit card or inserting money into a payment machine. Other innovative uses have also been proposed, such as allowing a refrigerator to track the expiration dates of the food it contains. How an RFID System Works RFID systems are composed of several components: tags, readers, edge servers, middleware, and application software. The key element of RFID technology is an RFID transponder, usually called a tag. An RFID tag is a small object, such as an adhesive sticker, that can be attached to or incorporated into an object (anything from a pallet of laundry detergent to a racecar tire to a pet's neck). An RFID tag is a tiny microchip composed of a processor, memory, and a radio transmitter that is mounted onto a substrate or an enclosure. The amount of memory varies from just a few characters to kilobytes. An RFID tag's antenna enables it to receive and respond to radio frequency queries from an RFID reader, also known as a trans- ceiver or an interrogator, which has its own antenna. Here's how an RFID system works (see Figure 15.8): 1. An RFID reader, which can interface through wired or wireless media to a main computer, transfers energy to RFID tags by emitting electromagnetic waves through the air. 2. RFID tag antennas collect the RF energy from the reader antenna and use it to power up the microchip. 3. Tags listen for a radio signal sent by an RFID reader. Chapter 