A good warning system serves two functions: Notify & Instruct.
Notify serves the function of getting the attention of a group of people in a specific place and at the right time. Once you have people’s attention you need to instruct them and give them the correct information on what to do.
Therefore, a good warning often consists of both a warning tone followed by a voice message. For example: Gas Alarm followed by the voice message “Gas Alarm – Go to Muster Area 2”.