tripwire

noun

1. A cord or wire arranged so that when snagged or pulled by an intruder, it will trigger a detector or trap or a device, such as a land mine.

   “Seeing the tripwire of a nearby bouncing Betty gave us cold chills, and we moved all the more slowly through the woods.”

   “They watched the two ghost-hunters run own the corridor and go crashing over the trip-wire.”

   “Thirteen people were injured in August 1957 when this Bristol freighter skidded on the runway at Southend Airport when landing with a flight from Calais. It ploughed through the boundary fence, but thankfully stopped short of the railway and the 1,500V overhead wires. A tripwire was installed on this section of Shenfield-Southend line to warn train drivers of instances such as this.”

2. (figuratively)Any means of detecting intruders or attackers.

   “The continued presence of U.S. troops as a tripwire force in Macedonia is an increasingly risky venture.”

verb

1. (transitive)To set a tripwire mechanism in (a location).