Emergency notification system

An emergency notification system refers to a collection of methods that facilitate the one-way dissemination or broadcast of messages to one or many groups of people "notifying" or alerting a group of individuals of a pending or existing emergency situation. Examples include; Mass text messaging services such as Twitter; mass automated dialing services such as Reverse 911 , and common siren systems that are used to alert for tornadoes, tsunami, air-raid, etc.