From the Hawaii Emergency Management Agency website
Hawaiʻi has the largest single integrated Outdoor Siren Warning System for Public Safety in the world. The all-hazard siren system can be used for a variety of both natural and human-caused events; including tsunamis, hurricanes, dam breaches, flooding, wildfires, volcanic eruptions, terrorist threats, hazardous material incidents, and more.
They test them here every month too. Shameful they didn't sound them when needed the most.
1000 as of earlier today.