The federal government may soon replace the five-color terror alert system with just two levels: “elevated” and “imminent.” The warnings would be sent out in part via Facebook and Twitter, according to a confidential draft proposal by the Department of Homeland Security obtained by the Associated Press. New alerts would also have expiration dates: 30 days for an “elevated” threat and seven for an “imminent” one, though they could be extended if the threat remains credible. The system also establishes procedures for issuing threat announcements and changing the threat level, which apparently there wasn't before. "It was pretty much kind of a gut call," said James Carafano, who was on a 2009 advisory committee to review the color alerts. The new system is expected to start by April 27.