Hotline

A hotline is a point-to-point communications link in which a call is automatically directed to the preselected destination without any additional action by the user when the end instrument goes off-hook. An example would be a phone that automatically connects to emergency services on picking up the receiver. Therefore, dedicated hotline phones do not need a rotary dial or keypad. A hotline can also be called an automatic signaling, ringdown, or off-hook service.

True hotlines cannot be used to originate calls other than to preselected destinations. However, in common or colloquial usage, a "hotline" often refers to a call center reachable by dialing a standard telephone number, or sometimes the phone numbers themselves.

This is especially the case with 24-hour, noncommercial numbers, such as police tip hotlines or suicide crisis hotlines, which are manned around the clock and thereby give the appearance of real hotlines. Increasingly, however, the term is found being applied to any customer service telephone number.

The most famous hotline between states is the Moscow–Washington hotline, which is also known as the "red telephone", although telephones have never been used in this capacity. This direct communications link was established on 20 June 1963, in the wake of the Cuban Missile Crisis, and utilized teletypewriter technology, later replaced by telecopier and then by electronic mail.

Already during World War II—two decades before the Washington–Moscow hotline was established—there was a hotline between No. 10 Downing Street and the Cabinet War Room bunker under the Treasury, Whitehall; with the White House in Washington. From 1943–1946, this link was made secure by using the very first voice encryption machine, called SIGSALY.

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