For the first time, the federal government will actually break into programming nationwide to test its emergency communications backbone. At approximately 2:00 pm EST on Wednesday, radio and TV stations will sound a loud tone and an announcement about testing the nationwide emergency alert system.

While most Americans have endured regular tests of this system by broadcasters on a state and local level, the federal government has never initiated a nationwide emergency alert.

The national EAS circuit, operated by the Federal Emergency Management Agency, allows the president to communicate with the public in an instant. On the president’s signal, FEMA can seize control of the airwaves temporarily and override the signal with the president’s message.