trip wire

Từ điển WordNet v3.1 - WordNet Dictionary

noun

1. 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
• Topics:
military, armed forces, armed services, military machine, war machine
• Hypernyms:
military unit, military force, military group, force
2. a wire stretched close to the ground that activates something (a trap or camera or weapon) when tripped over
• Hypernyms:
wire