• RFID devices encode an ID for tracking people, animals, and resources.rfid tags image by Albert Lozano from Fotolia.com
  
  RFID stands for Radio-Frequency Identification. This acronym also indicates a device using RFID technology to transmit an identifying number or code by radio to a reader.
  
  Such devices, called RFID tags or simply tags, perform a wide variety of services, such as controlling access, maintaining financial or medical records, identifying lost pets, tracking inventories, and securing shipping containers.
  
  RFID "chips" for embedded use may be no larger than a rice grain, and they may be packaged in larger containers with other components, such as batteries or sensors.
  
  

Passive RFID Devices

• Passive RFID tags send their IDs when queried by an RFID reader.safety trhough rfid image by Albert Lozano from Fotolia.com
  
  Passive RFID tags simply announce their IDs in response to a signal from a reader. They do not store other information. The reader software must look up the ID number in a database to translate the ID number into meaningful information, such as the date the tag was initialized with the number and a description of the identified resource. This ID number is loaded into the tag by computer.
  
  Passive devices are becoming less common as active RFID prices continue to fall.
  
  

Active RFID Devices

• Active RFID devices can send data to readers in response to a query.logistik image by Angelika Bentin from Fotolia.com
  
  Active RFID tags respond to queries from readers with their ID number and other information stored internally. Some active tags also have sensors that register environmental conditions, such as humidity, temperature, or pressure, and include this data--or excursions out of a specified range--when reporting to a reader. Other tags incorporate pressure switches that detect when a switch is released by the opening of a container door; this information is saved in the device's memory and can be retrieved at the time of the next read.
  
  

RFID Readers

• RFID readers query and monitor RFID devices for tracking and data collection.Wireless communications vector iconset image by Aleksandr Lukin from Fotolia.com
  
  RFID readers monitor responses from RFID tags but also initialize them and put them to sleep.
  
  Short-range readers provide a means to selectively "wake up" tags located near the reader so they can respond to queries without triggering responses from other devices out of the immediate area. RFID short-range readers can also monitor "chokepoints" to track RFID devices entering or leaving a secure area, again without polling other tagged resources. For example, hand-held readers can read the embedded tags in a cattle feed lot as each animal exits through a chute, beeping or making note of data stored in the tags concerning the date of vaccinations, genetic and medical history, and other details.
  
  Long-range readers are useful in warehouse or container shipping to quickly gather data about environmental conditions in different areas of a warehouse or to locate a container showing an open door quickly.