It's like a modern-day air raid siren.
Delivered to 225 million mobile devices, or 75 per cent of America's mobile phones, it comes with a noisy alarm and a text message, representing the latest incarnation of the doomsday warning that Americans might receive in the event of an imminent national emergency.
Think incoming nuclear missiles or a massive terrorist attack, a man-made disaster of epic proportions, a meteor or some other sort of nationally scalable natural disaster yet to be imagined.
A nightmare, basically.
TV broadcasts were also interrupted by the first test of the 'Presidential Alert' which is conducted by the Federal Emergency Management Agency (FEMA) under the WARN Act of 2006, which allows the President to commandeer communication networks to communicate in the case of nationally significant emergencies.
FEMA is required to test and maintain alert systems and says the aim is to "assess the operational readiness of the infrastructure for distribution of a national message and determine whether improvements are needed".
While it's the first national test of the new wireless emergency alert system, similar tests were conducted in 2011, 2016 and 2017.
Many Americans are familiar with the tone and vibration used, which is already in use for regional tornado and flash flood warnings, as well as amber alerts for missing children.
Americans can opt out of those, but the new national alert system does not allow for that.
It's described as "a national public warning system that provides the President with the communications capability to address the nation during a national emergency".
"In the event of a national emergency, a Presidential WEA alert would be issued at the direction of the President and/or his/her designee, and activated by FEMA," the agency says.
For residents of Hawaii, the alert may have jogged some frightening memories.
In January, after months of escalating exchanges between Mr Trump and North Korean President Kim Jong Un, the state's emergency personnel sent out an alert message reading, "BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL."
Officials estimate a missile would take less than 30 minutes to travel the 9,000-kilometre distance between North Korea and Hawaii, leaving residents with as few as 12 minutes to find shelter following detection and alert.
In January, as sirens sounded, people fled onto highways in their cars, hunkered down in their bathtubs and frantically texted their loved ones.
It took 38 minutes for the Emergency Management Agency to rescind the alert, which was the result of human error.
"Someone clicked the wrong thing on the computer," explained Richard Rapoza, a spokesman for the agency.
They've since created a "cancellation template" and instilled procedure requiring two officials to sign off before any alert is sent.
The alert was originally scheduled for last month but was delayed due to Hurricane Florence. Authorities were reluctant to test the system for an impending disaster while an actual disaster was unfolding.
It only lasted a moment, and then life went on.
