system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it that when dialing 911 it does not connect to another area code and always connects to a local one.
gpt
I'll assume you're talking about dialing from a mobile phone.

When you make a call from a mobile phone, the signal goes through a cell phone tower.  Every tower has a unique identifier, which is sent with your phone number, the number you're dialing, and some other information to a central office, which is a place where lots of phone lines (virtual or otherwise) come together and have calls routed between them.

So, let's say you dial 911.  And you're currently communicating with a tower named Jeff.  Jeff then talks to the central office and says:

> Hey, it's Jeff, and Koppite93 just dialed 911.

The central office knows where Jeff is - to within a few inches - and sends your call to the 911 office nearest Jeff.

More interesting is, sometimes 911 can see where *you* are using some of that information.

If you dial 911, the 911 dispatcher can also see that you're near Jeff.  Depending on the software they're using, they may see more detail - like that you're near Jeff, and he sees you with about 50% signal strength.  The software will call other towers, and find out if they can also see your phone's identifier.

If the towers Jeff, Dana, Kelly, and Winston all see you with roughly the same signal strength, because you know where they all are you can draw a circle around each, and where they all intersect is your approximate location.  That calculation is called triangulation.

Science is neat!