By Dina Fine Maron on September 20, 2018
Responding to fears of an imminent Soviet nuclear attack, in 1951 Pres. Harry Truman set up a national system enabling the president to quickly notify the public of an impending national security threat via a cross-country relay chain of AM radio stations. It used characteristic blaring warning tones and became a precursor of the Emergency Alert System still in use today. “There are certain stations across every market that listen for those tones and then retransmit the alert to other stations in their market,” says John Lawson, an emergency alert expert who has advised the Federal Emergency Management Agency (FEMA) on its modern warning systems.