(NewsNation) — The Federal Emergency Management Agency has scheduled a nationwide test of the emergency alert system for Oct. 4, sparking conspiracy theories online.

Here’s what you need to know about the test.

What is the emergency alert system?

The National Emergency Alert System is designed to alert people of potential dangers like severe weather or national emergencies like a nuclear attack. It’s also used for AMBER alerts and other types of alerts used for vulnerable missing persons.

The current system has been in place since 1997, but previous versions of an alert system have been in use since 1951 when President Harry Truman established CONELRAD, which used specific radio frequencies and was designed to warn citizens of a nuclear attack during the Korean War. In 1963, President John F. Kennedy established the Emergency Broadcast System, which continued to evolve as technology improved.

When will the test happen?

The nationwide test is set for Wednesday, Oct. 4, at around 2:20 p.m. ET.

Why are they testing it, and has it been tested before?

FEMA and the Federal Communications Commission are conducting the test to ensure the system is operational in the event of a national emergency.

This is the seventh test of the system, though it is only the second time cellphone alerts have been tested.

Is this test just for cellphones?

No. Emergency alerts will also be broadcast on televisions, radios and National Oceanic and Atmospheric Administration weather radios. If you have a lot of devices in your house turned on, it could get pretty loud.

What will happen during the test?

The alerts include a series of loud alarms meant to attract attention. These will go off even if devices are set to silent mode. The test will last for about one minute on radio and television, and cellphones should receive the alert within a half-hour of the test starting.

The test system will broadcast a message reading, “THIS IS A TEST of the National Wireless Emergency Alert System. No action is needed.” A translated message will be delivered for those whose language is set to Spanish.

What if there is an actual emergency during the scheduled test?

In the event of widespread severe weather, a backup test day is set for Oct. 11.

What if I don’t want my cellphone to go off?

While it is possible to opt out of some local emergency alerts, by law, carriers are not allowed to let customers opt out of national alerts. Even silenced devices will go off, though those in airplane mode should not receive the alert.

The inability to opt out may be a concern for people who have hidden cellphones, such as those in domestic violence situations. Erica Olsen, director of the Safety Net Project with the National Network to End Domestic Violence, said survivors may have hidden phones as part of a safety plan that allows them to communicate with others without an abuser monitoring what they are saying.

“If that device is powered on, then it could alert people and, in particular, the abusive person, of the existence of this device,” she said.

The only way to be sure those phones will not receive the test is to power off the device completely. For some older phones, this may include removing the battery entirely.

The FCC advises against opting out of public safety alerts in order to be aware of potential dangers of any kind.

If you are in a domestic violence situation and in danger, you can call a local hotline or the U.S. National Domestic Violence Hotline at 1-800-799-7233 and TTY 1-800-787-3224.

Has there ever been a case where the system was used for a real emergency?

The system is often used to send localized alerts for severe weather, like tornadoes or flooding. However, it has never been used for a national emergency.

What about false alarms?

In 2018, people in Hawaii received a false alert about a ballistic missile sent by a worker who believed the threat was legitimate. It took the state more than 30 minutes to issue a second alert letting people know the first was a false alarm.

Is the test connected to vaccines?

No. While conspiracy theories on social media have linked the planned test to debunked misinformation about vaccines, there is absolutely no connection between the two. The test poses no risk to human health, though the alert may startle those who are unaware of planned testing.