How 9-1-1 Works

Dialing 911 on a smart phone
Receive help during any life threatening situation. Kativ / Getty Images

­In May 2006, two children in Texas helped stop a four-man home invasion in progress in th­eir own home. That same month, a four-year-old boy helped save his mother's life when she started having an epileptic seizure, and a two-year-old beagle called for help when her person succumbed to a diabetic seizure - all by dialing nine, one and one on a telephone keypad (in the Beagle's case, she only pushed speed-dial number "9" and left the phone off the hook). These types of cases are an everyday occurrence at any 9-1-1 Public Safety Answering Point (PSAP) in the United States. Okay, the beagle thing was pretty rare, but still not unheard of.

­As of 2006, 99 percent of the U.S. population has 9-1-1 service. There are 200 million 9-1-1 calls per year in the United States, and 9-1-1 call-takers encounter a mind-boggling array of emergencies in their line of work. They must be prepared for almost anything. One operator in Florida picked up a call from a man who was in the process of choking. The call-taker walked the man through the process of performing the Heimlich maneuver on himself using the back of a chair, dealing with the situation in an incredibly calm, encouraging manner considering the circumstances. She told him, after one failed Heimlich attempt, "I want you to try to thrust upward right under your belly button. Can you do that? Come on, sweetie, try it for me." The man dislodged a piece of chicken and was able to breathe again before the dispatched firefighters made it to his house.


The idea behind 9-1-1 is pretty simple: Give people a single, easy-to-remember number to call to receive help during any life-threatening situation. There is no national 9-1-1 system. The answering points and corresponding dispatch services are set up and maintained locally, usually by county, often in a joint effort between local government and any phone companies active in the area. You pay for 9-1-1 with your local taxes and through a surcharge on your phone bill.

­ In order to be effective, any emergency system needs to do three basic things:

  1. recognize when someone dials the emergency number on any phone (even a pay phone when no coins have been supplied)
  2. route the call to the nearest answering point based on the call's originating location
  3. notify the appropriate agency as quickly as possible so it can respond to the emergency

­This is all that happens in basic 9-1-1 service. In enhanced 9-1-1 service, the answering point's equipment also automatically displays the caller's name and location, making step three above faster and more reliable. Enhanced 9-1-1 (E911) is not the same thing as wireless 9-1-1, but wireless 9-1-1 does require E911 improvements to be in place in order to work. The 9-1-1 system, which has always been based on the public switched telephone network (PSTN) that most of us use every day, has to adapt to constantly evolving technology, including the proliferation of cell phones, ­VoIP, and the introduction of safety measures like in-vehicle crash notification systems. Cell phones in particular have posed some big challenges to 9-1-1, and we'll get into that a bit later. For now, we'll focus on the 9-1-1 system in use when you dial out from a landline, which is still (but just barely) the most common way that people access a 9-1-1 answering point.

Call-taker at a 9-1-1 answering point (PSAP)
Photo courtesy U.S. Department of Transportation

The phone lines in use when you dial 9-1-1 are sometimes dedicated lines and switches intended to provide some additional security from outages and congestion, but they're still just regular phone lines. The PSTN system routes 9-1-1 calls to the Public Safety Answering Point (PSAP) nearest to where the call originated. The operator at the PSAP gathers information about the emergency and alerts the proper agency - the police, the fire department or emergency medical services (EMS), or sometimes all three.

In the next section, we'll take a look at what goes on behind the scenes to make all of this work as smoothly as possible.


Basic 9-1-1 Systems

As of 2006, approximately 7 percent of 9-1-1 service is still basic 9-1-1. Here's what this type of call looks like:

  1. You dial 9-1-1.
  2. Your phone company recognizes the number and routes the call to a dedicated 9-1-1 switch that sends the call to the designated PSAP for your area.
  3. The PSAP call-taker (also called an operator or dispatcher) asks what the emergency is, what the location is and for a call-back phone number. The call-taker does not have your number or location information on the screen. He or she actually needs you to provide it. (The PSAP can trace the call and get the information, but that takes longer than you'd think -- in the area of 10 minutes, in some cases -- because it's not built into the basic 9-1-1 system.)
  4. Depending on the emergency, the call-taker uses radio dispatch to alert police, fire and/or EMS to go to the scene.

­In most basic 9-1-1 systems, you're looking at several pieces of equipment (besides the PSTN) t­hat play a crucial role in the process. Some common 9-1-1 equipment includes:


  • Computer-controlled Radio Interface To more quickly dispatch emergency personnel, a PSAP might use a computer-controlled radio system to automatically activate electronic pagers.
  • Computer-aided Dispatch (CAD) A computer mapping program automatically provides directions to the caller's location and identifies any particular hazards or special information the responders might need to know (like road-work detours, flooded streets, that the caller is handicapped, etc.).
  • Recording Equipment PSAPs record everything, including phone calls and all radio communications into and out of the center. In most cases, the recorded data is stored for a minimum of 30 days in the event that police, prosecutors, PSAP managers or call-takers need to review the information. The CAD system can also serve as a full recording setup.
  • Back-up Power PSAPs have back-up generators and uninterruptible power supplies (UPS) in case of a power surges or outages. In most cases, PSAPs can stay online and operational even if the surrounding area has no power.

Next, we'll take a look at how E911 is different.


Enhanced 9-1-1 Systems

­Enhanced 9-1-1 is a very similar system, but it has some upgrades and modi­fications that make the whole process run more smoothly. There's more technology involved - in E911, there's a whole local "9-1-1 network" of collaborative databases that plays a role before the PSAP operator even picks up the call. For an E911 setup, add to the equipment list above:

  • Automatic Number Identification (ANI) The phone company knows every time you place a call from your phone number - it needs to know for billing purposes. This functionality is adapted to 9-1-1 purposes in E911: When you call 9-1-1 from your phone, the phone company recognizes the emergency number and uses the ANI system to pull up your phone number and send that data with your phone call to the 9-1-1 system.
  • Automatic Location Identification (ALI) The phone company has a subscriber database matching phone numbers to names and addresses. When your call arrives at the 9-1-1 network, the hub taps into this database to pull up the address that matches your phone number.
  • Master Street Address Guide (MSAG) The phone company and public safety agencies collaborate to create master maps that match phone numbers, addresses and cross streets to their corresponding PSAP. When you dial 9-1-1, the 9-1-1 network hub uses the MSAG to determine where to route your call.

As of 2006, 93 percent of 9-1-1 coverage is enhanced 9-1-1. Here's what the call looks like:


  1. You dial 9-1-1.
  2. The phone company computer recognizes the number, accesses the ANI to get your number and routes the call to the dedicated 9-1-1 switch that acts as a hub for the local network.
  3. The network uses your number to get your address from the ALI and uses your address to determine the proper PSAP destination from the MSAG (this is sometimes called selective routing, because the switch uses dynamic data to determine where to send your call instead of blindly routing it to a pre-determined PSAP). In most cases, this all takes a little over one second.
  4. Your phone call now carries your phone number and address along with your voice data to the nearest available PSAP. This information is displayed on the call-taker's computer when he or she takes your call.
  5. Some PSAPs simultaneously send that ANI/ALI data to the police computer dispatch network to allow for immediate access.
  6. If necessary, many PSAPs can transfer your call and your accompanying data to another PSAP.

When you're dialing from a landline, this system works really well. But when new phone technology enters the picture, a few hiccups emerge. The PSTN is not like a cell-phone network, and it's definitely not like a VoIP network. The rise of both of these types of phone service has placed demands on the 9-1-1 system to adapt in order to maintain an effective public-safety network.


Wireless Issues

As of 2006, more than 8 million people in the United States use a cell phone as their only phone­. Public-safety agencies report that wireless calls make up anywhere from 30 to 50 percent of 9-1-1 calls. Until recently, when someone called 9-1-1 from a cell phone, no information appeared on the call-taker's screen even in enhanced 9-1-1 systems, and the call wasn't always routed to the nearest PSAP to the caller's location. It could end up at any PSAP in the remote vicinity, depending on how the individual wireless provider had set up 9-1-1 routing. Local 9-1-1 systems have been implementing changes to 9-1-1 to allow for greater wireless compatibility, and upgrades are still happening now. The FCC has defined the upgrades in two phases:

  • Phase I: The call-taker can see the cell-phone number of the 9-1-1 caller and the location of the cell-tower antenna the phone is using. The call has been routed to the PSAP nearest to that tower. As of 2006, 83.6 percent of PSAPs have implemented all or part of Phase I. Phase I technology can only locate a cell phone within a 30-mile to 6-mile radius.
  • Phase II: The call-taker can see the cell-phone number and the location of caller to an accuracy of 50 to 300 meters depending the type of location system being used by the wireless provider. The call has been routed to the PSAP nearest to that location or nearest to the cell antenna in use, depending on the particulars of the system. As of 2006, 65.2 percent of PSAPs have implemented all or part of Phase II.

­There is no standardized method of implementing Phase II, so wireless providers, in conjunction with local public-safety agencies, are using various setups for providing cell-phone location information to PSAPs. There are two basic approaches: handset-based and network-based.


The handset-based solution is pretty straightforward. The phone you carry around has a full GPS receiver built-in, and when you dial 9-1-1 on the phone, the GPS receiver locates itself using satellites orbiting overhead. It taps into radio signals emitted by at least three satellites and times how long it takes the signals to reach the receiver. Using trilateration, the receiver can then determine its location (see How GPS Receivers Work to learn all about trilateration). What happens next varies with different systems, but one typical approach is pretty much a mobile mirror of the landline Enhanced 9-1-1 process. When your call reaches a cell phone antenna, the antenna sends not only your voice data and phone number, but also the latitude and longitude coordinates generated by the GPS receiver to the mobile switching station. The mobile switch either forwards the call to the dedicated 9-1-1 switch (the same ones used by landline calls) for PSAP routing or routes the call itself to the nearest PSAP, depending on the routing path the wireless carrier chooses. At the PSAP, mapping equipment (typically the CAD equipment discussed in the previous system) converts those coordinates to a street address that the call-taker can understand and provide to the dispatched emergency personnel. Verizon Wireless, Nextel, Sprint PCS and ALLTEL use a handset-based system.

The network-based solution is different from the handset method only in how the phone generate its latitude and longitude coordinates. A common implementation of network-based location-finding involves putting additional radio equipment on network base stations so that, in essence, they act something like a GPS receiver. When you dial 9-1-1 on your phone, the phone sends out radio signals to at least three of these towers, and the receiver in each tower times how long it takes for each signal to reach its receiver. Using trilateration (the same method used in GPS technology), the network can then pinpoint the location of the cell phone to an accuracy of 100 to 300 meters. Once the network has the latitude and longitude coordinates of the phone, it can send them with your voice call to the network switching station. AT&T Wireless, Cingular and T-Mobile use a network-based method.

While your cell phone almost certainly has basic 9-1-1 capabilities at this point (meaning you can dial 9-1-1 and reach a PSAP, even it's not the closest one to where you're calling from), implementing these wireless service improvements requires a collaboration between public safety agencies and all of the wireless carriers in your area, so it's a complicated process. Funding is often a problem, because both primary methods for generating cell-phone locations are pretty expensive, and there is no set rule about who should pay for the upgrades -- wireless-plan providers? Wireless-phone users? PSAPs? In at least one instance, a landline phone company has demanded a per-call routing charge for every wireless 9-1-1 call that ends up at the phone company's dedicated 9-1-1 switch.

In most cases, some combination of the involved groups funds the implementation of wireless 9-1-1 services; but in a lot of areas, there's just not enough money to do the upgrades. So it's not a slam-dunk that your call to 9-1-1 is going to be a smooth, Phase II experience. Also, depending on when you bought your handset, it may or may not be capable of taking advantage of these improvements (although most are by now). Call your wireless provider to find out which type of location-finding system it uses and whether your particular phone model is equipped to take advantage of the system.

If you have a serious emergency and you need to call 9-1-1 from your cell phone, play it safe -- remember, depending on where you are, there's about a 20 percent chance that the call-taker does not even see your phone number on his or her screen. The first thing you should do is tell the call-taker what and where the emergency is. Remember, there's about a 35 percent chance that the call-taker has no precise information about where you are. You must remember to provide the location information quickly, because if the call gets dropped early on and the call-taker doesn't have your number, he or she can't even call you back to get the location. Next, provide your cell phone number clearly so if the call does get dropped, the call-taker can call you back to continue helping you.

The recent rise in VoIP services has also led to some challenges for 9-1-1 service. We'll look at these next.


VoIP Issues

IP phone
Photo courtesy Consumer Guide Products

­Another technology that can cause problems in 9-1-1 emergencies is VoIP, or voice-over-Internet protocol. Some estimates have about 15 million people in the United States using VoI­P by 2008. When VoIP systems first gained popularity, there were some problems when it came to accessing 9-1-1 emergency services. Some VoIP customers reported not being able to reach 9-1-1 at all. In those cases, the VoIP provider often did not configure the individual system to access 9-1-1, which can take some tweaks. Sometimes the VoIP subscriber was supposed to specifically ask for full 9-1-1 access, a requirement buried somewhere in the small print of some service contracts. Usually, though, the problem was on the receiving end: The responding PSAP couldn't see the VoIP caller's location information because, in a sense, that phone number has no physical location.

Many VoIP systems are completely portable, working from any broadband connection -- in essence, the "phone number" is an IP address. As far as 9-1-1 is concerned, VoIP works totally differently from a regular telephone, and it works in numerous different ways depending on how the signal is being carried -- it could be via cable modem, DSL, T1, and a wired or wireless network, to name just a few varying parameters. In most home VoIP setups, voice signals start in the PSTN, switch to the Internet for the majority of their journey, and then get back on the phone lines. When, where or if the call gets routed to the dedicated 9-1-1 phone switch depends on the individual VoIP system. One system, Intrado's V9-1-1 Mobility Service, looks something like this:


The FCC has mandated that all VoIP providers include full, default access to 9-1-1 services (the customer doesn't have to request it) and that providers require a default physical location when setting up the account. This is the information that will be passed to the PSAP if you call 9-1-1 from that account.

It's unclear whether all VoIP providers have reached full FCC compliance at this time, so read your VoIP service agreement carefully to see if you need to give your service provider additional information (such as a default address) in order to have full 9-1-1 capabilities. Remember also that VoIP systems can go down if the power is out or your broadband connection fails, so you may want to get a generator to supply power to your VoIP phone line. You might also consider maintaining a regular phone line in the event that you can't call out from your VoIP phone.

In the face of new technology requirements, local 9-1-1 systems are undergoing some big changes. Some counties are starting to transfer 9-1-1 information via secure Intranet instead of relying only on phone lines. The digitization of data is the next step in 9-1-1 communications and will likely require a complete reformatting of the 9-1-1 infrastructure. This move would increase collaboration between emergency agencies by allowing for consistent information sharing and greater overall accessibility. In the far future, it could allow for the transfer of multimedia files, like a caller's cell-phone video clip of the emergency she's reporting, directly to the call-taker's computer screen.

Now that we've addressed the technology that makes 9-1-1 work, it's time to look at the rest of the equation: the people who make it work.


The Human Side

Photo courtesy U.S. Department of Transportation

­It may seem like a simple thing to determine when­ to call 9-1-1, but some PSAPs report between­ 15 and 20 percent of incoming calls as non-em­ergencies. So, what's a 9-1-1 emergency? A 9-1-1 emergency is a life-threatening situation in which every second counts. This includes serious medical issues, like a heart attack, uncontrolled asthma attack, seizure, child birth in progress, or anything involving large amounts of blood; any uncontained fire; and a life-threatening event like a knife fight outside a bar, an armed robbery in progress or a serious car accident (not a fender bender). Property theft is not considered an emergency, so if the armed robber has already left the scene, you can just look up the number for the police department instead of calling 9-1-1, since lives are no longer in danger. Neither a flat tire, a drunk person passed out in your bushes nor a serious desire to talk to someone about your recent divorce is considered a 9-1-1 emergency.

Even when there is a legitimate emergency and a caller is right to call 9-1-1, the call doesn't always go smoothly. Some mistakes that callers make include calling 9-1-1 and then leaving the phone or just hanging up, assuming the operator has all the necessary information when in fact he or she may have no information at all. Callers often hang up too soon during a call, causing the call-taker to have to call back to confirm details and make sure help has arrived. One big but often unavoidable problem occurs when the caller is hysterical and the call-taker can't understand what the caller is saying, in which case obtaining accurate information takes a lot longer than usual. And sometimes, callers don't pay enough attention to their environment to provide the location information the call-taker needs.


In June 2006 in Pennsylvania, six-year-old Brandon Bennett got it right. He watched his grandmother go into diabetic shock and immediately called 9-1-1, putting in motion the series of events that would save her life. With the help of the 9-1-1 call-taker, Brandon made a proper 9-1-1 call, which looks something like this:

  • Dial 9-1-1 and wait for operator to pick up. The operator will say, "911. What's your emergency?"
  • Stay on the line, speak clearly and follow the operator's instructions.
  • If possible, be aware of your surroundings so you can tell the operator exactly what's happening and where it's happening. The more information a call-taker has, the better he or she can help you by sending exactly the response team and equipment you need.
  • Don't hang up until the call-taker tells you to -- if you hang up too early, before the issue is resolved or before the call-taker knows that emergency personnel have arrived, she'll just have to call you back.
Photo courtesy Morguefile/Michael J Summerville

­Call-takers are trained to ask the right questions, calm hysterical callers and get emergency personnel to the scene as quickly as possible. In an emergency situation, none of these is necessarily an easy task. In May 2006 in Warrensburg, Missouri, a 9-1-1 call-taker picked up a call and heard nothing but a barely audible "Help me, help me." This went on for five minutes while the call-taker was trying to get some sort of information from a clearly debilitated caller so he could send help. The caller was using a cell phone, and this PSAP had not yet implemented Phase II, so the call-taker had nothing but a very vague general location and a call-back number. Five minutes into the call, all communication stopped. It sounded like the caller had lost consciousness.

The operator remained diligent. He stayed on the line for 20 minutes, listening intently to nothing but some background noise and, finally, a smoke alarm, until the woman regained consciousness for long enough to provide some partial address information. The call-taker dispatched emergency personnel to the apartment building the woman indicated, and they knocked on doors until they heard their own knocking through the radio link to the PSAP. They found the right apartment and rescued a 21-year-old, unconscious pregnant woman who likely would have died from smoke inhalation if she'd remained undiscovered for much longer. An unattended pot on the stove had filled the apartment with smoke and was ready to produce a fire at any minute.


911 Mistakes

­Call-takers need to be able to handle a tremendous variety of issues with patience and expertise. They receive training in crisis response not only in terms of demeanor, but also in crisis management tools and in the actual things that need to happen when police, fire and paramedics respond to an emergency. The 9-1-1 call-takers know what they need to ask in order to get the first responders there safely and fully equipped to handle the situation. Further training may involve:

  • 9-1-1 technology and equipment
  • police, fire and EMS procedures
  • questioning techniques
  • hazardous materials (what are they, where might they be and how would the caller be able to identify them)
  • legal liability issues
  • radio verbalization
  • cross-cultural issues (knowing what to expect and how to respond to callers from different cultural backgrounds)
  • stress management

­Even with extensive training, call-taker mistakes happen. And when the mistake is regarding a 9-1-1 call, the consequences can be devastating. One instance of 9-1-1 human error that received national attention is that of the 9-1-1 calls made by a five-year-old boy in Detroit in February 2006. Robert Turner called 9-1-1 when his mom, Sherrill Turner, collapsed from heart problems. The call-taker thought he was making a prank call and asked for an adult, and when Robert said he couldn't get an adult on the phone, the call-taker said she'd send help and hung up. But help didn't arrive. Three hours later, his mom still unconscious, Robert called 9-1-1 again. This time, a different call-taker answered, but it was the same result -- the call-taker thought it was a kid playing around, and she told him he'd get in trouble if he kept it up. Robert got scared and hung up. His mom died, although no one is sure exactly when. Both operators have been indicted on charges of willful neglect of duty and could face jail time. Robert's family is filing a wrongful death suit against the city because they believe that if the first operator had properly responded to Robert's call, Sherrill Turner would still be alive.


Not all call-taker mistakes are so devastating and unimaginable, but the fact is, when someone calls 9-1-1 and the person who picks up is not on the ball, bad things are going to happen. In Astoria, Oregon, in October 2005, a call-taker dismissed a call reporting a fire -- she simply asserted there was no fire, that it was just "the play of light in the rain and fog." It wasn't until another person called 9-1-1 15 minutes later to report the same blaze that firefighters were dispatched to the area, and by that time there was nothing they could do.

It's likely that most call-taker mistakes can be attributed to stress. Handling life-threatening emergencies all day is not an easy task, and call-takers can experience severe job-related stress issues. Some eventually suffer from critical incident stress syndrome (CISS), a condition something like post-traumatic stress disorder (PTSD) but it affects people who are constantly close to and intricately involved in other people's massive crises and tragedies. CISS can cause symptoms like severe anxiety, nightmares and an inability to cope with stressful situations in daily life. Most PSAPs offer not only training in stress management, but also have psychologists or social workers available for call-takers who need help dealing with the stress of their job.


Lots More Information

Related HowStuffWorks Articles

More Great Links


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