Today, sirens will blast in wavering unison to a sound not heard in Hawaii since the Cold War — an “attack warning.”

In this case, it’s what Hawaii residents can expect to hear in the remote case of a North Korean attack.

The sirens are set for testing at 11:45 a.m. statewide.

Normally, on the first business day of each month at that time, the state tests the steady-tone “attention alert” that is meant for threats such as hurricanes or tsunamis. That siren tone is used to notify the public of any emergency that may pose a threat to life or property. It’s a cue for residents to turn on a radio or television for information and instruction for an impending emergency.

With the threat of a North Korean attack, the state is adding the wavering-tone warning siren.

Vern Miyagi, administrator of the Hawaii Emergency Management Agency, formerly Civil Defense, said the attention alert siren will be sounded for about 50 seconds, followed by a pause of about 15 seconds, followed by the wavering, or wailing, attack warning siren.

Audio messages will accompany the siren tests and refer to the new tone. “It is critically important for the public to understand what each tone means,” Miyagi said at a presentation Tuesday.

The attack warning means people should seek immediate shelter in the most substantial structure possible because a North Korean missile would arrive in Hawaii just 20 minutes after launch.