From the foothills of the Rocky Mountains, the North American Aerospace Defence Command (NORAD) scrutinises the skies for threats such as missile attacks and hijacked planes.
But for the next 24 hours, NORAD will not just be monitoring all aircraft, missiles and spacecraft with its network of satellites, ground and airborne radar and fighter jets. The US and Canadian military will also track the global flight path of a distinctive red-clad individual on a sleigh and his team of reindeer, for the entertainment of children around the world.
Deploying the latest social media tools, NORAD's Christmas Eve Santa Tracker is expected to hit another record this year, bolstered by an unusual dose of controversy about the "militarisation" of the season.
Last year, the operation attracted 22 million website visits, 1.2 million Facebook followers, 950,000 smartphone downloads and 129,0000 Twitter followers as well as 114,000 telephone calls.
Unsurprisingly, the most popular questions are variants of "where is Father Christmas and when is he arriving at my house?". (© Daily Telegraph, London)