RFID

RFID, or radio-frequency identification, uses small radio tags that a reader picks up without contact. The FASTag on a car's windscreen, a tag fixed to a pallet in a warehouse and the chip in a library book are all examples. A tag holds a short identity number. The reader reads the number from a distance of a few centimetres to several metres.

Here is how it works in general. A tag contains a tiny chip and an antenna. A reader sends out a radio signal. The signal gives the tag enough energy to wake up and reply with its number, so most tags need no battery. The reader passes the number to software, which looks up what the number stands for, such as a vehicle, a parcel or a person's badge, and records the time and place. Unlike a barcode, the reader does not need to see the tag, and it can read many tags at once.

Tags differ by the radio band they use. Low-frequency and high-frequency tags, such as access cards, metro cards and library books, work from a few centimetres. Ultra-high-frequency tags, such as those on FASTag and on warehouse cartons, work from several metres. A passive tag has no battery. An active tag has a battery, a longer range and a higher price. Metal and liquids disturb radio waves, so a tag on a metal can may need a special design. A tag costs a few rupees, and a simple one can be copied, so high-value uses add a security code.

Take, for example, a toll plaza. A reader above the lane reads the FASTag on a car travelling at 30 km/h, and the toll is debited from the linked account; see electronic tolling. Consider a warehouse where a worker pushes a trolley of cartons past a gate, and the reader counts all of them in one pass; see the warehouse floor. Imagine an office door that opens when a badge is held near it; see physical access control.

RFID is also an important tool for track and trace, and it works together with cameras, as described in ANPR.

How is it different from a barcode or a QR code? A barcode must be seen by a scanner, one at a time. An RFID tag is read by radio, without line of sight, and many tags can be read together.