This is a fairly complicated technical scenario and it gets more and more complicated depending on whether there are multiple locations that are geographically separated all sharing one phone system. For example, a school district with multiple grade, junior high, and high schools. You do not want to send notifications to the high school when someone at the grade school dials an emergency number. Further, while a phone call is nice, and overhead paging is good, in noisy manufacturing environments maybe you need multiple channels -- phone call, email, SMS, and desktop popup. The hope being that one of the four channels will be received.
I could also see the need/benefit of having an emergency number you define that only generates notifications internally, but does not send notices to the emergency responders (PSAP), while other emergency numbers send notifications to both internal and external emergency responders.
Then there is the whole question about how to implement panic buttons and repeating alarms. If I see a tornado from my window is about to hit the building, I do not want to dial an extension, what for the ring group to be ready, say the warning, all while the tornado gets closer and closer. No, I want to hit a button and run for the shelter and let the system "say" the warning.
How about logging the events that capture when the emergency took place, who was notified and how, and maybe have a place to add notes about the incident so if you get sued later, you have careful notes about who did what and when.
Finally, what if you have mobile people who move from place to place with their laptops and they dial an emergency number from their web client? Where do we send the emergency responders, to their official desk location, or do we figure out where they are within our campus of buildings and make sure we send responders to the correct place.
I realize I've taken the original question and expanded on the topic well beyond their specific question, but handling emergency notifications correctly is a topic that requires careful consideration. Maybe, if you have one building, and you do not care where the person was that dialed the emergency number, then perhaps it is as simple as calling a multi-cast paging ring group with the paging dial code. But I think a more robust solution is probably warranted.
I encourage you to take a look at our
3CX Emergency Notifier tool. We have a new version about to be released with lots of new enhancements and a significantly improved UI which makes a great tool even better.