RFID (Radio Frequency Identification) is a technology for transferring information without physical contact. The data is stored in “tags”. RFID is used to track goods, in electronic locks, theft alarms, electronic tickets for public transit, etc. A simple case is a fixed number stored in a tag, which is then used in a similar way as barcodes. More advanced tags have integrated microprocessors.
RFID tags have no internal power supplies, instead they take their power from an electromagnetic field output by tag readers. This is converted into the correct voltage in the tag, which can transmit its data to the reader.