red box

Short definition from Wiktionary

Noun

1. 1
   A phreaking device that generates tones to simulate the insertion of coins into a payphone, thus enabling the user to make illegitimate free calls.
2. 2
   A secure briefcase-like box used by ministers in the British government to carry their documents.
3. 3
   A safe located at a nuclear installation containing launch codes.
4. 4
   A "tornado watch" notification, indicating that conditions might lead to a tornado though none has yet been sighted.