The truth - and fiction - about today's emergency alert test

A test of the US emergency alert system on Wednesday won't cause phones to buzz for half an hour straight.

It is not a secret signal which will trigger World War Three.

And it won't turn people who've received Covid vaccines into zombies.

Although these facts may seem too odd to even mention, millions have seen rumours like these circulating online about the routine test scheduled to begin at 14:40 EST (19:40 GMT).

In reality, the test of the national Emergency Alert System (EAS) and Wireless Emergency Alerts (WEA) system will cause most mobile phones to buzz for a short time.

TV and radio broadcasts will be also be briefly interrupted.

Local tests of TV and radio alert systems have been happening for decades. While nationwide tests of the broadcast system began in 2011, today's test marks only the second time the test message will be blasted out to all compatible cell phones across the country, according to the Federal Emergency Management Agency (Fema).

These same alert systems are activated for real in the event of a natural disasters or other emergency. The harsh, attention-grabbing tone will be familiar if you live in an area with frequent tornados or hurricanes, for instance.

Some of the online rumours started with a misunderstanding. The message testing window is 30 minutes long, according to Fema, leading some to conclude that their phones will buzz for that entire period of time.

However, if the test works correctly, each phone will be alerted just once, and pressing a button on your phone or dismissing the alert will silence the test - although in previous tests some people have reported getting the message multiple times.

Other rumours were spread by conspiratorial accounts - with an assist from people mocking them.

One post on X, viewed more than 5 million times and mocked by thousands, claimed the test "using 5G" will "activate the Marburg virus in people who have been vaccinated. And sadly turn some of them into zombies".

The post, which was debunked by the site's Community Notes feature, seemed to be a mash up of a number of Covid pandemic conspiracy theories, and quickly became an easy target for sarcasm.

"This is a joke tweet, right?" one user asked.

Similar false rumours about the test "activating nanoparticles" were also swirling on TikTok, Facebook, YouTube and other social networks.

If past experience is a guide, the rumours will swiftly go away following the test - until Fema announces the next one.