The federal government on Wednesday implements a new terror alert system that will replace the color-coded terror alerts put in place after the September 11, 2001, terrorist attacks.

"The National Terrorism Advisory System, which was developed in close collaboration with our federal, state, local, tribal and private sector partners, will provide the American public with information about credible threats so that they can better protect themselves, their families, and their communities," Homeland Security Secretary Janet Napolitano said in a statement.

While the color-coded system had five levels of alerts, the new NTAS will have only two - "elevated threat," which "warns of a credible terrorist threat" to the U.S., and "imminent threat,"  which "warns of a credible, specific and impending terrorist threat," according to a Department of Homeland Security statement.

Any alert will automatically expire after a specific time, although alerts could be extended if new information shows a threat persists, DHS said.

DHS released a sample alert that shows how future releases will be formulated.

The department is asking the public to watch for any suspicious activity, incorporating the New York Metropolitan Transportation Authority's trademark slogan "If You See Something, Say Something" into its alerts.

"We know that the best security strategy is one that counts on the American public as a key partner in securing our country," Napolitano said in the statement.

Looking at how the two systems would rate U.S. security today, Wednesday, April 20, the DHS website says under the old system the threat level is "elevated, or yellow;" under the new system, it lists no alerts.