Guam - Joint Information Center Advisory: 

The Governor directed the Emergency Operations Center to stand up an audible alert siren system throughout the island. The Guam Police Department has constructed this siren system. If there is an emergency, you will hear this siren system from your house or your work in every village of the island. The siren system is the sound of a police siren, with an amplified voice message that says, "This is a national emergency. Shelter in place." If you hear this, it means the Governor has ordered the island in RED condition and you should IMMEDIATELY shelter in place. For more information on how to shelter in place, please refer to FACT SHEET 2, which is attached.
The Joint Information Center produced a video depicting this siren alert system so Guamanians know what to listen for in the event of an emergency http://www.youtube.com/watch?v=zUeFaZSpA5o&feature=youtu.be