A tag and a reader
Radio-frequency identification, or RFID, uses radio communication between a tag and a reader to identify an item. A typical tag combines a small chip with an antenna. The reader receives data from it.
NIST describes the different RFID tag types. The important starting point is the pair: a tag is a data carrier, and a compatible reader is needed to communicate with it.
Follow one shirt
Imagine a shop attaching an RFID tag to a shirt. A reader detects the tag’s identifier, and the shop’s software uses that identifier to find the associated record.
The tag is not the whole shop database. Reading an identifier and looking up information about the item are separate steps. The exact information available depends on the system.
An optical barcode needs its printed pattern to be visible to a scanner. RFID does not need that direct optical line of sight. As GS1 US explains, readers can detect suitable tags within their reading range.
Where does the energy come from?
A battery-free passive tag gets energy from the reader’s electromagnetic field. That energy lets its circuitry respond. A small label can therefore work without a battery inside it.
Other RFID designs use an internal power source. Active tags and battery-assisted designs are reasons not to assume every RFID tag works in exactly the same way.
No direct line of sight does not mean unlimited range. The tag and reader still need to communicate successfully. Compare the radio exchange with a QR code’s visible grid, then continue through Read the codes around you.