The alert, to be broadcast at 1 p.m. Houston time, will not display graphics stating the familiar "this is a test" message on some stations because of their technical limitations.
Although accompanying audio will clarify that the alert is a test and authorities have initiated a sweeping campaign to inform the public about it, the pervasive nature of the midday announcement and the lack of clarity for some TV viewers could cause problems.
"While this is only a test, we are concerned that if a citizen hears or sees this on all TV stations, they could be concerned or confused and then ultimately call 911 to find out what is going on," said Sonya Clauson, a spokeswoman for the Greater Harris County 9-1-1 Emergency Network, which operates 40 call centers in Harris and Fort Bend counties.
Bracing for calls
Many Americans regularly misuse 911 and erroneously call the emergency line simply for information, Clauson said. That could dramatically increase during confusion about a national crisis and has left officials worrying about actual emergency calls not getting through, she said.
"I'm thinking the confusion will be minimal, but we have such a large media market that even a small level of confusion could result in an increase in calls that overwhelm the 911 system," said Francisco Sanchez, spokesman for the Harris County Office of Homeland Security & Emergency Management.
The office will open a command center Wednesday with representatives from various agencies that could respond to any inquiries created by confusion about the alert.
It's not clear when a national emergency alert would be used. It would not have been used for 9/11, the Cuban missile crisis, or for any event over the last 50 years, said Jamie Barnett, chief of the Federal Communication Commission's public safety and homeland security bureau.
In most cases, mass media were able to adequately inform citizens and worked as conduits for officials to communicate with the public.
Cyber or missile attack
There are modern threats - movie-like scenarios - that could conceivably draw a national alert.
A cyberattack that might knock out the nation's power grid would be one example, Barnett said. In that situation, an alert sent over radio waves could reach people with battery-powered devices.
Or perhaps a major impending missile strike or a devastating attack where an alert system could be used to assure citizens that the government is still working, he said.
"You can imagine that there might be some times when they would need it," Barnett said. "It is a national asset."
But to ensure that residents don't think the warnings on every channel they flip through Wednesday afternoon are real, officials have asked TV broadcasters to tell viewers about the alert in advance.
"We're going to warn people on either side of it," said Tom Ash, a spokesman for KTRK. Ash said the station would probably receive calls from confused viewers.
3-minute try scrapped
But the overall concern from the 30-second test will not be as worrisome as the initially proposed three-minute version.
That test would have enabled a series of other diagnostics to run but would have increased the potential for mass confusion at the sight and sound of an alert on every TV and radio station for that entire span. Officials later determined they could run those other tests within their labs.
The 30-second test will still allow government officials to see how the full national effort works and determine where the system can be improved, Barnett said.
Officials are planning to expand alert systems to cell phones in 2012, allowing owners of those devices to sign up for alerts.
Those alerts would warn users who were within affected geographical areas or nationally.
"It gives that kind of same irritating noise that you hear on the TV," Barnett said.
"It'll definitely get your attention."