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.
(..) Go, go! Go! Is he back? Keep your eyes open. Go, go. Cover the doors! Where's your trigger?! Where is it?! You'd never give it to an ordinary citizen! Where is it? Where's your trigger?! (..)2012 The Dark Knight Rises
(..) And at the first sign of interference from the outside world... or from those people attempting to flee... this anonymous Gothamite... this unsung hero... will trigger the bomb. Return to your homes... hold your families close... and wait. Tomorrow, you claim what is rightfully yours. (..)2012 The Dark Knight Rises