The emergency number 911 is the universal number for emergencies but 911 only works for emergencies in the USA.
911 the phone number was established and put in place in the year 1967 which is when the Federal Communications Commission (FCC) met with AT&T to establish such a short and easy to remember number to be called in emergencies.
However when you're out of the United States the number 911 will not work and you'll need to dial 112 especially if you're in Europe.