trigger
nounUK /ˈtrɪɡ.ər/
US /ˈtrɪɡ.ɚ/
The part of a gun that you pull to make it fire.
He put his finger on the trigger.
OTHER MEANINGS
2. Something that causes something else to happen.
The loud noise was a trigger for her headache.
3. To make something start or happen suddenly.
The news triggered a big argument.
4. A device that starts a machine or process.
The alarm has a trigger that sets off the siren.