red box

noun4

1. •
   (UK) A secure briefcase-like box used by ministers in the British government to carry their documents.

   • Downing Street has rejected suggestions that David Cameron might have caused a security breach by briefly leaving his official ministerial red box unaccompanied on the table of a train carriage. — 2013
2. •
   (US, informal) A "tornado watch" notification, indicating that conditions might lead to a tornado though none has yet been sighted.
3. •
   A phreaking device that generates tones to simulate the insertion of coins into a payphone, thus enabling the user to make illegitimate free calls.
4. •
   (US) A safe located at a nuclear installation containing launch codes.