Police officers are trained to not be too 'quick on the trigger'. [=eager to fire a gun]
The timer was set to 'trigger' the bomb in exactly one hour.
The faulty wire was the 'trigger for' the explosion.
(..) - It's us. - Jesus. It isn't a lockdown, is it? Or a riot? No. Hal, for God's sakes, just take your finger off the trigger. Are you hostages? Who's out there? - Who's by that truck? - Harry, the lights! John Coffey. (..)1999 The Green Mile