"Our officers are among the most highly skilled of any commercial office building, regularly receiving training from the City of Chicago, the Bureau of Alcohol Tobacco and Firearms, the Secret Service and the FBI on topics ranging from how to detect people with ill intent, how to spot and react to a suspicious packages and how to respond to a fire until the Chicago Fire Department arrives," Carley says.

In the years subsequent to 9/11, there have been a number of security threats made on the tower. But building management and security officials, who "regularly speak with the FBI and local law enforcement authorities," say they have implemented many measures--both visible and behind-the-scenes--to protect the building.

Carlos Villarreal, vice president of National Security and Life Safety with Trizec Properties, was head of security at the Sears Tower in 2001. He says Sept. 11 changed the way businesses operated across the country. "I knew my life had changed that day; the plans we had in place were not sufficient enough to get us through the new threats," he tells GlobeSt.com. The first thing building management did, he says, was to step up the number of security officers. With both tenants and building management demanding fast resolutions, "the first 90 days were brutal," he says.