FEMA and the FCC plan to conduct a massive test of Emergency Alert System (EAS) and Wireless Emergency Alerts (WEA) Wednesday.

The test will involve every cell phone in the US, as well as radios and TVs:

The national test will consist of two portions, testing WEA and EAS capabilities. Both tests are scheduled to begin at approximately 2:20 p.m. ET on Wednesday, Oct. 4.

The WEA portion of the test will be directed to all consumer cell phones. This will be the third nationwide test, but the second test to all cellular devices. The test message will display in either English or in Spanish, depending on the language settings of the wireless handset.

The EAS portion of the test will be sent to radios and televisions. This will be the seventh nationwide EAS test.

FEMA says the test will help ensure the system can handle national emergency warnings:

The purpose of the Oct. 4 test is to ensure that the systems continue to be effective means of warning the public about emergencies, particularly those on the national level. In case the Oct. 4 test is postponed due to widespread severe weather or other significant events, the back-up testing date is Oct. 11.