Code Nine was a priority alarm initiated when computer software — activated on the release of the Emergency Protocols — detected important words.

When Jackie Tyler phoned the BBC alien helpline and told them about the Ninth Doctor and his TARDIS, the words were highlighted and a Code Nine was declared. Indra Ganesh informed General Asquith of this development. Asquith did not understand as he was really a Slitheen impersonating the General. (TV: Aliens of London)

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