Changes

Sometimes your you're building is Courthouse, or a Market, or a Factory, and the entire ''point'' is that the general public goes in and out of the building all the time. In such a circumstance, all the divination magic in the world doesn't mean anything because your enemies can actually just walk into your building to scout the place for a teleport ambush or even buff themselves up on the outside and then run in while 1/round a level spells are counting down their awesome. In these circumstances, you're going to want a fall-back position to be readily available on little or no notice. Contingent magic and magical traps may well want to pull key personnel ''out'' rather than send summoned monsters or impediments ''in''. After all, if you put off the final confrontation for 20 minutes, the teleport ambush has essentially failed.