It’s not often that any one of us needs to dial 911, but we know how important it is for it to work when one needs it. It is critical that 911 services always be available – both for the practicality of responding to emergencies, and to give people peace of mind. But a new type of attack has emerged that can knock out 911 access – our research explains how these attacks occur as a result of the system’s vulnerablities. We show these attacks can create extremely serious repercussions for public safety.