tripwire

/ˈtrɪpˌwaɪər/
noun
  1. A wire or cord stretched close to the ground that triggers a trap or alarm when someone trips over it.
    • The security system uses a tripwire that sounds an alarm when disturbed.
    • They set up a tripwire around the campsite to alert them if any animals came near.
    • The soldier carefully avoided the tripwire hidden in the grass.
  2. Something that causes an immediate reaction or response, often a negative one.
    • The politician knew that raising taxes would be a tripwire for voters.
    • For her, the word 'failure' was a tripwire that made her feel anxious.
    • Any mention of the accident was a tripwire for his anger.
Synonyms
What does "tripwire" mean? | whatsthatwordmean | whatsthatwordmean