tripwire
/ˈtrɪpˌwaɪə(r)/noun
1- a wire stretched close to the ground, working a trap, explosion, or alarm when disturbed and serving to detect or prevent people or animals entering an area绊网; 引爆线; 警报拉发线。
1.1
- a comparatively weak military force employed as a first line of defence, engagement with which will trigger the intervention of strong forces前哨试探性部队（较弱的第一道防线部队, 与此部队交战将导致强大部队的介入）。