US unveils new terrorism warning system

In announcing the new system at New York City's Grand Central Terminal, commonly known as Grand Central Station, Napolitano said a main goal was to provide better understanding of the nature of the specific threat, what people should do in reaction to it and how they could help security officials in responding.

"It will provide alerts based on specific, credible information about potential terrorist activity," Napolitano said, adding that the alerts would contain "as many details as we can provide."

Right now, she said, there is no threat that would reach the level to warrant one of the new alerts, which will take effect on April 26.

(...) The new system has two levels of alerts, compared to the previous system's five levels, Napolitano said.

The two alert levels of the new system are "elevated threat," which "warns of a credible terrorist threat" to the United States; 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 two-week period, although they could be extended if new information shows a threat persists, DHS said.

Napolitano told reporters in a morning briefing that the alerts posted on a department website -- www.dhs.gov/alerts -- will provide details to show the nature, location and other information about terrorism threats. Therefore, she said, a specific warning may apply to a particular address, community, city or region, rather than the non-specific general warnings of the color-coded system.

Alerts also will be announced by her office and made public via traditional media such as television announcements and radio broadcasts, as well as social media, Napolitano said.