In many countries the public telephone network has a single emergency telephone number (sometimes known as the universal emergency telephone number or occasionally the emergency services number) that allows a caller to contact local emergency services for assistance. The emergency number differs from country to country; it is typically a three-digit number so that it can be easily remembered and dialed quickly. Some countries have a different emergency number for each of the different emergency services; these often differ only by the last digit. In the European Union, '112' was introduced as a common emergency call number during the 1990s, and as the GSM standard it is now a well known emergency number across the globe alongside the North American '911' and the British '999'.

Configuration and operation

The emergency telephone number is a special case in the country's telephone number plan. In the past, calls to the emergency telephone number were often routed over special dedicated circuits. Though with the advent of electronic exchanges these calls are now often mixed with ordinary telephone traffic, they still may be able to access circuits that other traffic cannot. Often the system is set up so that once a call is made to an emergency telephone number, it must be answered. Should the caller abandon the call, the line may still be held until the emergency service answers and releases the call.

An emergency telephone number call may be answered by either a telephone operator or an emergency service dispatcher. The nature of the emergency (police, fire, medical) is then determined. If the call has been answered by a telephone operator, they then connect the call to the appropriate emergency service, who then dispatches the appropriate help. In the case of multiple services being needed on a call, the most urgent need must be determined, with other services being called in as needed.

Emergency dispatchers are trained to control the call in order to provide help in an appropriate manner; they can be assisted by computer aided call handling systems (CACH). The emergency dispatcher may find it necessary to give urgent advice in life-threatening situations. Some dispatchers have special training in telling people how to perform first aid or CPR.

In many parts of the world, an emergency service can identify the telephone number that a call has been placed from. This is normally done using the system that the telephone company uses to bill calls, making the number visible even for users who have unlisted numbers or who block caller ID. For an individual fixed landline telephone, the caller's number can often be associated with the caller's address and therefore their location. However, with mobile phones and business telephones, the address may be a mailing address rather than the caller's location. The latest "enhanced" systems, such as Enhanced 911, are able to provide the physical location of mobile telephones. This is often specifically mandated in a country's legislation.

Operator assistance

When an emergency happened in the pre-dial (or "manual") telephone era, the user simply picked up the telephone receiver and waited for the operator to answer "number, please?" The user responded with "get me the police," "get me the fire service," or "I need an ambulance/doctor." Even in large cities, it was seldom necessary to ask for these services by number.

In small towns, operators frequently provided additional service, knowing where to reach doctors, veterinarians, and law enforcement personnel at all times. Frequently, the operator was also responsible for activating the town's fire alarm.

When manual switching systems began to be replaced by automatic, or "dial" systems, there was frequently concern among users that the very personalized emergency service provided by manual operators would be lost.

Because numbers were different for every exchange, callers either had to dial the operator or look up the telephone number. An example of this was Auckland, New Zealand before the introduction of 111 in the 1960s – the city had 40 exchanges, all with different emergency numbers, and finding the telephone number for the local exchange would require having to search through the city's 500-page telephone directory.

This problem was at least partially solved in the United States, Canada, and the UK by dialling "0" for the local assistance operator in case of emergency, although faster service could be obtained if the user dialled the full number for the Police or Fire Department. This system remained essentially unchanged throughout most of North America until the 1970s.

Direct-dial numbers

The first emergency number system to be deployed anywhere in the World was in London on 1 July 1937 using the number 999, and this was quickly extended to cover the entire country. When 999 was dialled, a buzzer sounded and a red light flashed in the exchange to attract an operator's attention.

Because of loop disconnect dialing, attention was devoted to making the numbers difficult to dial accidentally by making them involve long sequences of pulses, such as with the UK 999 emergency number. However in modern times, where repeated sequences of numbers are easily accidentally dialled on mobile phones, this is problematic, as mobile phones will dial an emergency number while the keypad is locked or even without a SIM card.[citation needed] Some people have reported accidentally dialing 112 by loop-disconnect for various technical reasons, including while working on extension telephone wiring, and point to this as a disadvantage of the 112 emergency number, which takes only four loop disconnects to activate.

Southern California Telephone Co. began using 116 as an emergency line for Los Angeles, California in 1946. The emergency number 999 was adopted in Winnipeg, Manitoba, Canada in 1959 at the urging of Stephen Juba, mayor of Winnipeg at the time. The city changed the number to 911 in 1972, in order to be consistent with the newly adopted U.S. emergency number.

The first 911 emergency phone systems went into use in Alabama and Alaska in 1968.The first 911 call was made in Sacramento, California on February 10, 1968. The second system, in Nome, Alaska was put into service later that same month. However, 911 systems were not in widespread use until the 1980s when the number 911 was adopted as the standard number across most of the country under the North American Numbering Plan.

The implementation of 911 service in the USA was a gradual and haphazard process. Because telephone service boundaries did not always exactly match governmental and other jurisdictional boundaries, a user might dial 911, only to discover that he had been connected to the wrong dispatch center because he had telephone service from one location but lived within the boundaries of another jurisdiction.

Electromechanical switching equipment still in use made it difficult to adapt to recognize 911, especially in small towns and rural areas where the call might have to be switched over a considerable distance. For this reason, it is still not unusual for a county sheriff's department to have a toll-free "800" area code number.

Gradually, various problems were overcome; "smart" or "enhanced" 911 systems were developed that not only would display the caller's number and address at the dispatch center but also could be configured so that 911 calls were automatically routed to the correct dispatch center, regardless of what central office the caller was served from. In the United States, most cities have E911 systems either in use, or in their emergency systems design plans.

The rapid replacement of electromechanical switching systems in the 1980s with electronic or digital systems eliminated the problem of older switches that would not recognize 911. At this point, 911 service is available in most of North America, but there is still the occasional small, remote town that does not have it.

In France, many telephone exchanges were closed at night but it was still possible to make emergency calls. An operator had to connect the emergency calls only. In 1913, an automatic system was set up. It made provision for calling the police by dialling 17 and the fire brigade by dialling 18. As more manual telephone exchanges were converted to dial operation, more and more subscribers had access to these special numbers. The service was not widespread until the 1970s.

The CEPT recommended the use of 112 in 1972. The European Union subsequently adopted the 112 number as a standard on 29 July 1991. It is now a valid emergency number throughout EU countries and in many other CEPT countries. It works in parallel with other local emergency numbers in about 2/3 of EU states.

In January 2008, the Internet Engineering Task Force released a set of RFC documents pertaining to emergency calls in IP networks.

Emergency numbers and mobile telephones

Mobile phones can be used in countries with different emergency numbers. A traveller visiting a foreign country does not have to know the local emergency numbers, however. The mobile phone and the SIM card have a preprogrammed list of emergency numbers. When the user tries to set up a call using an emergency number known by a GSM or 3G phone, the special emergency call setup takes place. The actual number is not even transmitted into the network, but the network redirects the emergency call to the local emergency desk. Most GSM mobile phones can dial emergency calls even when the phone keyboard is locked, the phone is without a SIM card, or an emergency number is entered instead of the PIN.

Most GSM mobile phones have 112, 999 and 911 as pre-programmed emergency numbers that are always available. The SIM card issued by the operator can contain additional country-specific emergency numbers that can be used even when roaming abroad. The GSM network can also update the list of well-known emergency numbers when the phone registers to it.

Using an emergency number recognized by a GSM phone like 112 instead of another emergency number may be advantageous, since GSM phones and networks give special priority to emergency calls. A phone dialing an emergency service number not recognized by it may refuse to roam onto another network, leading to trouble if there is no access to the home network. Dialing a known emergency number like 112 forces the phone to try the call with any available network.

On some networks a GSM phone without a SIM card may be used to make emergency calls and most GSM phones accept a larger list of emergency numbers without SIM card, such as 112, 911, 118, 119, 000, 110, 08, and 999. However, some GSM networks will not accept emergency calls from phones without a SIM card, or even require a SIM card that has credit. For example, Latin American networks typically do not allow emergency calls without a SIM. Also, GSM phones sold in some countries like Singapore do not accept 112 as an emergency number even if they have a SIM card inserted.

The GSM phones may regard some phone numbers with one or two digits as special service codes. It might be impossible to make an emergency call to numbers like 03 with a GSM phone.

In the United States, the FCC requires networks to route every mobile-phone and payphone 911 call to an emergency service call center, including phones that have never had service, or whose service has lapsed. As a result, there are programs that provide donated used mobile phones to victims of domestic violence and others especially likely to need emergency services.

Mobile phones generate additional problems for emergency operators, as many phones will allow emergency numbers to be dialed even while the keypad is locked. Since mobile phones are typically carried in pockets and small bags, the keys can easily be depressed accidentally, leading to unintended calls. A system has been developed in the UK to connect calls where the caller is sent to an automated system, leaving more operators free to handle genuine emergency calls.