Chips in RF tags can be read-write or read-only. With read-write chips, you can add information to the tag or write over existing information when the tag is within range of a reader, or interrogator. Read-write tags are useful in some specialized applications, but since they are more expensive than read-only chips, they are impractical for tracking inexpensive items. Some read-only microchips have information stored on them during the manufacturing process. The information on such chips can never been changed. A more flexible option is to use something called electrically erasable programmable read-only memory, or EEPROM. With EEPROM, the data can be overwritten using a special electronic process.