A tripwire is a passive trigger
-Technology:* Trigger , a mechanism that actuates the firing of firearms* Image trigger, a device used in highspeed cameras* Schmitt trigger, an electronic circuit* Trigger circuit, IBM's name for a flip-flop...

ing mechanism. Typically, a wire or cord is attached to some device for detecting or reacting to physical movement. From this basic meaning, several extended and metaphorical uses of the term have developed.

Metaphorical usage

The Berlin Brigade
Berlin Brigade
After the end of World War II, under the conditions of the Yalta and Potsdam agreements, Allied forces occupied West Berlin. This occupation lasted throughout the Cold War...

 stationed in the divided city of Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...

 during the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

 was given the mission to be the "tripwire" for a Soviet incursion into West Germany
West Germany
West Germany is the common English, but not official, name for the Federal Republic of Germany or FRG in the period between its creation in May 1949 to German reunification on 3 October 1990....


Literal usage

Military usage may designate as a tripwire the wire attached to one or more mines
Land mine
A land mine is usually a weight-triggered explosive device which is intended to damage a target—either human or inanimate—by means of a blast and/or fragment impact....

 — normally bounding mine
Bounding mine
A bounding mine is an anti-personnel mine designed to be used in open areas. When tripped, a small propelling charge launches the body of the mine 3-4 feet into the air, where the main charge detonates and sprays fragmentation at roughly waist height....

s and the fragmentation type — in order to increase their activation area. Alternatively, tripwires are frequently used in boobytraps, whereby a tug on the wire (or release of tension on it) will detonate the explosives.

Soldiers sometimes detect the presence of tripwires by spraying the area with Silly String
Silly String
Silly String is a children's toy of flexible, sometimes brightly-coloured, plastic string propelled as a stream of liquid from an aerosol can. The solvent in the string quickly evaporates in mid-air, creating a continuous strand. Silly String is often used during weddings, birthday parties,...

. It will settle to the ground in areas where there are no wires; if there are any, the string will be suspended in the air but not set them off due to its light weight. It is being used by U.S. troops in Iraq for this purpose.
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