A system aboard starships whose single purprose is to destroy the ship. Usually used to prevent bad guys from capturing the ship.
Usuallt requires at least 2-3 senior officers to activate, although on Voyager, Janeway could do it on her authorization alone.
Computer, initiate auto destruct sequence, authorization Janeway PI Alpha 47. Set at 5 minute silent countdown ... enable.
Computer: Bleeeep, auto destruct system enaged, warp core overload in 4 minutes 55 seconds. There will be no further audio warnings.