The service is very straightforward -- users can text their locations and emergency to 911 and police or fire services will be dispatched accordingly. It is imperative that users send their location, as a text message cannot be traced like a phone call.
The service is only available in a few select regions and the Federal Communications Commission advises that people do not rely on the service and that in most cases people will not be able to contact 911 using the texting service.
Those who attempt to contact 911 in locations where the service is not available will receive a return message informing them of that fact. But the carriers have committed to switching to the text-to-911 service wherever the call centers are able to receive these types of calls.
Select counties in Colorado, Georgia, Illinois, Indiana, Iowa, Maine, Maryland, Montana, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Texas, Vermont, and Virginia have started the service.
The FCC says the service could be helpful when "a voice call to 911 might otherwise be dangerous or impossible." These could be instances where making a noise could reveal your location to an intruder.
But despite the service it seems more advisable to call 911 when possible as first responders always prefer to have more information than can be shared in a text. Responders also like to gauge the disposition of a caller, which can point to things like mental states and possible medical conditions.