Get ready, it's coming. On Wednesday, Oct. 4 at 2:20 p.m. ET/11:20 a.m. PT, your cellphone, radio or TV will blare a jarring electronic noise that signals a test of the nationwide Emergency Alert System (EAS).
This is a coordinated effort between the Federal Emergency Management Agency (FEMA) and the Federal Communications Commission (FCC) to test the Integrated Public Alert and Warning System (IPAWS).
It could be postponed to Oct. 11 if there's severe weather or other significant events, according to FEMA.
The process involves two parts: a 30-minute signal sent to radios and televisions as part of EAS, and a similar one sent to all consumer cellphones as part of the WEA system.
Federal law requires the systems be tested at least once every three years. The last nationwide test was Aug. 11, 2021.
According to FEMA spokesperson Jeremy Edwards, the audio signal used for the tests utilizes the same combination of tones familiar to Americans since 1963, when President John F. Kennedy established the original Emergency Broadcast System through an executive order. It's also the same tone that more than 1,700 local, state, territorial and tribal authorities use to send similar alerts for more localized emergencies.
Last month, a conspiracy theory about health impacts of the test spread on social media.
Stanley Perlman, professor of microbiology and immunology at the University of Iowa in Iowa City, said the claims appear to be referring to old myths about the contents of COVID vaccines. These baseless conspiracy theories claim - without evidence - that the vaccines contain various materials, such as graphene oxide or other nanoparticles, that can interact with wireless communications technology and allow governments to control and monitor people.
But graphene oxide - a material made by oxidizing graphite - isn't an ingredient in COVID vaccines, notes Matthew Laurens, a pediatric infectious disease specialist with the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine.
"Graphene oxide was used to study vaccine structure only, and is not part of the vaccine formulation," he wrote in an email.
Regardless, the notion that graphene oxide can be "activated" in this way is "nonsense," wrote Julia Greer, a materials science professor at the California Institute of Technology in Pasadena who has used graphene oxide in her research, in an email.
"You can't 'activate' graphene oxide," she wrote. "What does that even mean?"
The actual nanoparticles in the vaccines, meanwhile, are lipids, or fats, that are generally used as a coating material. They're sometimes described as "programmable" because they can be modified and adjusted, depending on the need, experts have said. It does not mean they can be programmed to interact with wireless networks.
There's also nothing nefarious about the routine test FEMA and the Federal Communications Commission are conducting Wednesday. Such tests have been happening with regularity for years now without any reports of adverse health effects from the system signals, said Edwards.
ABC News and Associated Press writer Philip Marcelo in New York contributed this report.