RFID tags are tiny microchips with memory and an antenna coil, thinner than paper and some only 0.3mm across! RFID tags listen for a radio signal sent by a RFID reader. When a RFID tag receives a query, it responds by transmitting its unique ID code and other data back to the reader. There are two types of RFID tags:
Passive RFID tags. Passive RFID tags can be as small as 0.3mm and don't require batteries. Rather, they are powered by the radio signal of a RFID reader, which "wakes them up" to request a reply. Passive RFID tags can be read from a distance of about 20 feet. Semi-passive RFID tags contain a small battery that boosts the range. Passive tags are generally read-only, meaning the data they contain cannot be altered or written over.
Active RFID tags. Active RFID tags, also called transponders because they contain a transmitter that is always "on", are powered by a battery, about the size of a coin, and are designed for communications up to 100 feet from the RFID reader. They are larger and more expensive than passive RFID tags, but can hold more data about the product and are commonly used for high-value asset tracking. Active RFID tags may be read-write, meaning data they contain can be written over.