Volunteers are pulling on their Santa hats, phone lines are set, and tracking screens are ready - NORAD Tracks Santa is primed for its 57th annual goodwill mission.
    
Santa trackers start taking calls early Monday, telling children - and some adults - when Santa is due at their house. The last shift won't end until nearly 24 hours later.
    
The number is 877-HI-NORAD or 877-446-6723.
    
Updates will be posted online (http://www.noradsanta.org), on Facebook (http://www.facebook.com/noradsanta) and Twitter (https://twitter.com/NoradSanta).
    
The operation is based at Peterson Air Force Base in Colorado Springs, Colo., home of the North American Aerospace Defense Command.
    
NORAD Tracks Santa began in 1955 when a newspaper ad listed the wrong phone number for kids to call Santa. They wound up calling the Continental Air Defense Command, NORAD's predecessor.