Place it at the start of a defensive setup or just before a Bastion ambush in a highlight, then follow it with Enemy Spotted for the callout and Bomb Has Been Planted when the objective pressure peaks. Keep it as the warning that sets up the action, not the payoff after it.
About this sound
This is a short spoken warning, lasting about two and a half seconds, in which a voice urgently tells teammates to watch out because they have a Bastion. The delivery is clipped and alert, with the emphasis landing on the danger rather than on a joke. It feels tense and watchful, like a callout made in the middle of a fight, when every second of warning counts.