By Mike WendlingBBC News
Watch: Blaring test alert disrupts business as usual in DCA test of the US emergency alert system on Wednesday didn't cause millions of phones to buzz for half an hour straight.
It was not a secret signal that triggered World War Three.
And it didn't turn people who've received Covid vaccines into zombies.
Although these facts may seem too odd to even mention, millions saw rumours like these circulating online prior to the routine test which began at 14:40 EDT (19:40 GMT).
In reality, the test of the national Emergency Alert System (EAS) and Wireless Emergency Alerts (WEA) system caused most mobile phones in the US to buzz for a short time.
TV and radio broadcasts were also briefly interrupted.
Local tests of TV and radio alert systems have been happening for decades. While nationwide tests of the US broadcast system began in 2011, today's test marked only the second time the test message was 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 disaster or other emergency. The harsh, attention-grabbing tone is 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 was 30 minutes long, according to Fema, leading some to conclude that their phones would buzz for that entire period of time.
However each phone was meant to receive the alert just once, and pressing a button or dismissing the alert silenced the test - although in previous tests some people have reported getting the message multiple times. On Wednesday, many people reported receiving the test message two minutes ahead of schedule.
Getty ImagesHow the alert message looked during a test in 2018Other rumours were spread by conspiratorial accounts - with an assist from people mocking them.
False rumours about the test "activating nanoparticles" swirled on TikTok, Facebook, YouTube and other social networks.
One post on X, viewed more than 5 million times and mocked by thousands, claimed the test "using 5G" would "activate the Marburg virus in people who have been vaccinated. And sadly turn some of them into zombies".
The post, 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. The mockery continued after the most dire predictions about the test failed to come true.
"So what's the next great conspiracy we have to look forward to now that the great zombie apocalypse was a dud," one post read.
A 2018 test of the system prompted other baseless claims - including that then-President Donald Trump would use the system as a way to send out political messages.
The rumours about the emergency system largely went away following Wednesday's test - at least until Fema announces the next one.
BBC in other languagesInnovationncG1vNJzZmivp6x7o67CZ5qopV%2Bjsri%2FjrCmq6SUYsK0ecKapZqckWKDd4WYaW5scQ%3D%3D