A Hawaii Civil Defense Warning Device, which sounds an alert siren during natural disasters, is shown in Honolulu on Nov. 29, 2017. The alert system is tested monthly, but now Hawaii residents will hear a new tone designed to alert people of an impending nuclear attack by North Korea.

A Hawaii Civil Defense Warning Device, which sounds an alert siren during natural disasters, is shown in Honolulu on Nov. 29, 2017. The alert system is tested monthly, but now Hawaii residents will hear a new tone designed to alert people of an impending nuclear attack by North Korea.