In January 2005 McCarran began offering complimentary Wi-Fi throughout its passenger terminals. The service initially covered , making it the largest free Wi-Fi zone among U.S. airports at the time. The northeast wing of the D Gates opened in April 2005, along with a air traffic control tower at the center of the concourse. The expansion had been postponed following the September 11 attacks but resumed amid high growth in passenger traffic. Later in the year, the airport started a baggage-tracking system using radio-frequency identification (RFID) tags. Small RFID transmitters are inserted into baggage tags to improve bag identification, thereby lowering the risk for lost or misplaced luggage. McCarran became one of the first airports worldwide to conduct RFID tagging on a large scale.