Since the 1950s, the U.S. government has helped kids and kids at heart follow Santa on his annual Christmas Eve trek across the globe. But how did the tradition of tracking Santa’s flight get started?

According to the North American Air Defense Command’s website, the tradition started in 1955 after an advertisement for Sears Roebuck & Co. misprinted a telephone number for children to call Santa. The incorrect number was the hotline for the Continental Air Defense Command commander-in-chief’s operations group.

The director of operations, Colonel Harry Shoup, had staff members check radar for evidence of Santa making his way south from the North Pole. Children who called the number were given updates on his location, and a tradition began.

Since then, NORAD staffers have volunteered their time to take phone calls, answer emails from children across the world and use the Internet to track Santa’s whereabouts on Christmas Eve.

On Christmas Eve, follow along with Santa’s journey on NORAD’s live blog.