A thin wire pulled tight low across a path, so that anyone walking there catches a foot on it without seeing it. It is part of a trap. In war and in films, a tripwire is attached to a bomb or a mine, and the pull sets it off; hunters use them for animals; a camp might rig one to cans so the noise gives a warning. The wire is the trigger, and the whole point is that it is invisible until it is too late. English also uses the word for things that are not wire at all. In politics and business, a tripwire is a small event that automatically sets off a much bigger response — "a tripwire for sanctions" means the moment a country does that one thing, the punishment starts by itself, with no further argument. Soldiers stationed in a country are sometimes called a tripwire force for the same reason: they are too few to win a war, but attacking them would drag in a whole alliance. Keep the picture of the hidden wire and both uses make sense.

絆線（陷阱或地雷的觸發線）；引申指「一碰就自動引爆後果的臨界點、觸發條件」