CNN 2011-01-02（在线收听）

Three, two, one, Happy New Year!

A rehearsal in Time Square of the ball drop to ring in the New Year as thousands crowd around it to watch. Behind the scenes, the New York City's Police Department is gearing up for a massive security operation.

This is sort of a nerve center.

New York City Police Commissioner Ray Kelly says the department updates its plan each year to secure crowds who must be within barricades and go through metal detectors. Radiation detectors are also used. And backpacks are banned.

We're concerned about a device that someone might bring in on their person, a vehicle borne device, a vest of some sort, explosives on the body.