Universal emergency number?

Well, kind of. In Europe, it's "112". But, that number doesn't work in the US. Here, of course, it's 911. Even if your cell phone doesn't have service anymore, if you have power and a signal, you can still dial 911 at anytime. So, it's a good idea to keep an old phone charged up and in your glove compartment for emergencies. And, that's no myth. This could be one time when a cell phone can save your life.
If you travel outside US, you must contact the local authorities or neighborhood to check the correct emergency number for that country.