RFID differs from barcodes in that it does not require line of sight to be read.

Tags generally fall into two categories - passive and active. Both types typically consist of a microchip attached to an antenna which is usually mounted on a substrate. Active tags  have a battery while passive tags rely on the power that comes from the electromagnetic fields used to read them. In general, the further the distance the tag is from the reader, the more power will be needed to transmit the information. 

Different types of tag work on different radio frequencies, so the choice of tag will come down to the application they are being used for. There are international standards for these frequencies to prevent conflict with other wireless technologies.

Typical chips can store up to 2 Kb of data. This means they can carry additional information such as date of manufacture, shipment date, destination and sell-by date as well as identity.

For tags to be useful, there have to be readers. A typical reader is a device that has one or more antennas that emit radio waves and receive signals back from the tag. The reader then passes the information in digital form to a computer system.