This signal is first discovered when the Sole Survivor activates the relay dishes at relay tower 0BB-915. The source of the signal can then be tracked to a ham radio inside a military bunker at the base of the southwestern satellite at the Fort Hagen satellite array.
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This is a message from the Commonwealth of Massachusetts Emergency Alert System. This morning, Saturday October 23rd, authorities detected that a nuclear attack had commenced against the United States. The following cities affected include, but are not limited to: Washington, DC; New York; Philadelphia; and Boston. If you are receiving this emergency alert message, immediately seek shelter that can provide protection from radioactive fallout. This has been an emergency action notification.
This has been a pre-recorded message. Message repeats in three seconds.
The Civil Alert System broadcast appears only in Fallout 4.