30th June 1937: World's first emergency telephone number began operation

The number 999 was first introduced on this day in 1937.

This happened in London, and the mentioned number became the first emergency telephone number in the world. Before that, in case of emergency, the typical procedure was as follows: people would dial zero, an operator would answer the phone, and connect the caller to the required service (like an ordinary telephone call).

But operators were busy with ordinary calls, and emergency calls had to wait without any priority. After the introduction of 999 number, the procedure was changed: when people dial 999, a red light and specific sound would suggest that is an emergency call, and operators have to give priority to answering the phone.

But why was the number 999? At the time, people had to turn a telephone dial to get a number. In the dark or in dense smoke, 999 could be dialed by placing a finger one hole away from the dial stop, and rotating a dial to the full extent three times. On the other hand, the number 111 could be dialed accidentally, including when transmission wires made momentary contact produce a pulse similar to dialing.

Today, when people use touchscreen phones, the number 999 is not so good, and can be dialed by mistake. Thus, the emergency number 112 is used in Europe, and 911 in the USA. It is interesting to note that the number 999 is still used in the UK (for emergency calls), in addition to 112.
http://history.info/on-this-day/1937-the-worlds-first-emergency-telephone-number-999/
https://en.wikipedia.org/wiki/Emergency_telephone_number

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