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112 is the common emergency telephone number that can be dialed free of charge from most mobile telephones and, in some countries, fixed telephones in order to reach emergency services (ambulance, fire and rescue, police).
This choice of number has the following advantages:
Different digits: with the numeric keypads used universally today, using at least two different digits instead of the same digit repeatedly significantly reduces the risk of accidental calls. Young children, vibrations, defective keys and collisions with other objects are much more likely to press the same key repeatedly than a particular sequence of different keys, particularly with a button-operated keypad. Accidental calls to emergency centres from mobile phones, which can dial emergency numbers even with locked keypad, are a particular problem with same-digit numbers, such as the UK’s 999.
Low digits: in the days of rotary dial telephones, using only those digits that require the least dial rotation (1 and 2) permitted a dial lock in hole 3 to effectively disable unauthorised access to the telephone network without preventing access to the emergency number 112. The same choice also maximised dialling speed. Additionally, telephone systems used pulse dialling instead of later DTMF tones; briefly activating the hook once has the same effect as dialling “1”, so repeatedly pushing the hook might result in calling 1-1-1. For this reason, Germany’s police emergency number was changed from 111 to 110. With numeric keypads, pressing only the first and second button on the keypad is marginally easier in a difficult situation than other keys.