Place it at the end of a slow build, just before the reveal, then follow it with the FNAF Jumpscare Scream for the payoff. For a larger trailer moment, stack it after the Inception Horn Sound Effect and let the reveal land on the second hit.
About this sound
This is a brassy blast from a Westinghouse E2-B1 train horn, lasting just over four seconds, with a hard opening that grows into a long, ringing chord. It feels tense and alarming, turning a calm scene into a warning that something large is about to appear. It became the signal for the Neon City animatronics in the FNAF D-Day fangame, after fans borrowed the railway horn from Trainz simulator circles.