How the 911 Emergency Call System Really Works

The 911 emergency system was inaugurated in the 1960s, but its rollout was slow, and it took years for smaller towns to fund and implement it. We all knew it was a great idea. Then enhanced 911 came out, and they could locate your landline phone as soon as you called. What sorcery is this? But technology advances, and now cities with the most sophisticated 911 service can even locate the cell phone that made the call. 

We rely on the system, but few of us understand how it works now. Half as Interesting explains what happens when you make a 911 call. I have a bone to pick, though. Back in the day, you never had to dial a ten-digit number to get the local police. That would be a useless long-distance call. Local numbers are seven digits, or four digits if you go back far enough. This video is only 5:27; the rest is an ad. 


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Yes, the multiple insistence on 10 digit numbers got to me too, especially when it shows a phone with the number WHitehall 4-9970. Oh! Bensalem Township, PA got a new phone number in 1953, Cornwells 1138, and the police in Elmonte, Calif's was Gilbert 8-6191 according to an article about and ad pranking the police. In the 1935 murder-mystery The House on the Roof the police number was simply 1313.

Looks like in 1970 some 40,000 calls per day to the police were made through the operator, which the Bell System promoted as the backup universal emergency code. "There will always be operator assistance available for emergency calls."

The last time I called the operator was in 1991, and last operator assisted call I did was in 1988.
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Back in the 1990s I had a co-worker who used to work on the E-911 for the Chicago area. He told me there was a db config error once, which caused all the call to get routed to one center.
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Years ago I was the senior engineer for the company that ran half of the US E-911 system (50% chance your voip/cell 911 call would be routed by us). I'm afraid there was nothing very exotic about it... mostly just a bunch of racks of commodity computers (servers) doing the heavy-lifting. The video mentioned determining cellphone location from GPS and cell tower triangulation, but glossed over the next step of turning it into a state/city/street/address (reverse-geocoding). I was involved with upgrading that to be faster and more accurate. You can imagine the amount of testing required for any changes to that system...
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