PETERSON AIR FORCE BASE, Colo. (AP) — Volunteers have pulled on their Santa hats, and are answering phone lines and monitoring wall-size tracking screens as NORAD Tracks Santa begins its 57th annual goodwill mission.

The first shift of Santa trackers started taking calls early Monday at 877-HI-NORAD (877-446-6723), telling children — and some adults — when Santa is due at their house. The last shift won’t end until nearly 24 hours later.

They’ll also post updates online (http://www.noradsanta.org), on Facebook (http://www.facebook.com/noradsanta) and Twitter (https://twitter.com/NoradSanta).

The volunteers are working from Peterson Air Force Base in Colorado Springs, Colo., home of the North American Aerospace Defense Command.

NORAD, a joint U.S.-Canada command responsible for protecting the skies over both nations, says its Santa-tracking rite was born of a humble typo in a newspaper ad in 1955.

The ad in a Colorado Springs newspaper invited children to call Santa but inadvertently listed the phone number for the Continental Air Defense Command, NORAD’s predecessor, also based in Colorado Springs.

CONAD officers played along, and word spread that this Cold War military command charged with guarding the U.S. against an attack by the Soviet Union was also telling kids where Santa was.

Since then, NORAD Tracks Santa has gone global, progressing through bulletins on AM radios and black-and-white TVs to updates on Facebook, Twitter and smartphone aps.

Last year, volunteers answered almost 102,000 calls, nearly 25 percent more than the previous year. They also answered more than 7,700 emails (noradtrackssanta(at)outlook.com).

The NORAD Tracks Santa website attracted 18.9 million unique visitors from 220 countries and territories during December 2011.

This year, the program has more than 1 million likes on Facebook and more than 114,000 followers on Twitter days before the tracking operation got under way.

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Follow Dan Elliott at http://twitter.com/DanElliottAP

Copyright 2012 The Associated Press.