The notification was sent to mobile handsets as a trial, with the Federal Emergency Management Agency (Fema) eager to determine whether the previously unused system would work as it was intended.
In a real-life emergency, the system would only be triggered by the order of US President Donald Trump.
The alert would be used in very specific circumstances, including if the US was facing the threat of missile attacks, acts of terrorism and natural disasters.
However, the system has faced efforts to have its usage blocked by a journalist, a breastfeeding advocate and a fitness instructor.
The trio warned that the system is vulnerable to abuse.
Their legal action explained: "Officials - including [President] Trump - are free to define 'act of terrorism' and 'threat to public safety' as they see fit, potentially broadcasting arbitrary, biased, irrational and/or content-based messages to hundreds of millions of people."
Despite this, a New York judge dismissed their action on Wednesday (03.10.18), meaning Fema was free to press ahead with the Presidential Alert.
The system was mistakenly used earlier this year to warn citizens of a missile attack against Hawaii.