You can put a collider for the monster, and one for the player who activates the monster
void OnStart
{
AddEntityCollideCallback("Grunt_1", "AreaGruntDeact", "CollideAreaGruntDeact", true, 1);
AddEntityCollideCallback("Player", "AreaGruntActive", "CollideAreaGruntActive", true, 1);
}
void CollideAreaGruntActive(string &in asParent, string &in asChild, int alState)
{
SetEntityActive("Grunt_1", true);
AddEnemyPatrolNode("Grunt_1", "PathNodeArea_1", 0, "");
}
void CollideAreaGruntDeact(string &in asParent, string &in asChild, int alState)
{
SetEntityActive("Grunt_1", false);
PlaySoundAtEntity("", "SOUNDNAME", "DOORNAME", 0, false);
}