WordNet
n. a small military force that serves as a first line of defense; if they become engaged in hostilities it will trigger the intervention of stronger military forces
a wire stretched close to the ground that activates something (a trap or camera or weapon) when tripped over
Usage examples of "trip wire".
Then the AK put a few rounds across our front and the platoon went down as if they had hit a trip wire.
He knew where there was a trip wire laid that fired a set-gun and he located it in the dark, stepped over it, and started along the small stream bordered with poplars whose leaves were moving with the night wind.
But affer you'd seen your first trip wire set off by someone else—.
Meanwhile, Bronstein was furiously organizing, and Eamon was fiddling with last-minute touches on a trip wire attached to the limpet-mine on the jammed trailer.
Spotting the assassin, they swung around to fire on him as they ran toward him, setting off an unnoticed trip wire.
The trip wire would set off the mine and spew out over two hundred small ball-bearing-like projectiles in a cloud of death.
They angled the mines for the best killing effect, set the trip wire on the first one, then on the second.