FORT WORTH - All 153 warning sirens in the Fort Worth system blasted people out of bed at 1:34 am Thursday.
Some wailed for 30 seconds. Others for two minutes or more.
Social media lit up as residents awoke to the blaring noise and authorities began to receive calls from concerned citizens.
"Are we under air raid attack," wrote John Bacon on Twitter. "What's up with the sirens."
911 operators told them there was no emergency, but they didn't know what was going on.
One man startled by the sirens never did get back to sleep.
"I'm the emergency management coordinator for the City of Fort Worth," Juan Ortiz said.
He rushed to the new Emergency Management Center downtown.
"We secured the system within 30 minutes and silenced all the alarms," he said.
Basically, Ortiz said he switched the system from "ready" mode to "standby." Then he started troubleshooting.
"It looks like one of our controllers had a malfunction, and issued a command to activate all sirens," he said.
The device that apparently failed is about the size of a computer keyboard. Ortiz said the installer and manufacturer have been notified.
As of late Thursday afternoon, there was still no explanation for why the controller sent out the activation signal.
"This is our top priority," Ortiz said. "We want to find out why the system failed so that we can prevent it from happening again. We have never experienced this before."
Ortiz said workers spent the day trying to replicate the problem, and that it might require sending the box back to the manufacturer to be analyzed.
Ortiz does not believe hackers tampered with the system, because it's not tied to the internet. It uses radio signals.
He said the system can be quickly reactivated if there's a real emergency.
In case of emergencies, including tornadoes, large hail or chemical spills, Fort Worth notifies residents by text through Nixle. Registration is free at