NORAD Santa Tracking System

From the NORAD site:

It all starts with the NORAD radar system called the North Warning System. This powerful radar system has 47 installations strung across Canada's North and Alaska. NORAD makes a point of checking the radar closely for indications of Santa Claus leaving the North Pole on Christmas Eve.

The moment our radar tells us that Santa has lifted off, we begin to use the same satellites that we use in providing warning of possible missile launches aimed at North America. These satellites are located in a geo-synchronous orbit (that's a cool phrase meaning that the satellite is always fixed over the same spot on the Earth) at 22,300 miles above the Earth. The satellites have infrared sensors, meaning they can see heat. When a rocket or missile is launched, a tremendous amount of heat is produced - enough for the satellites to see them. Rudolph's nose gives off an infrared signature similar to a missile launch. The satellites can detect Rudolph's bright red nose with practically no problem. With so many years of experience, NORAD has become good at tracking aircraft entering North America, detecting worldwide missile launches and tracking the progress of Santa, thanks to Rudolph.

Cool.