Hmm. I took out the turret monitors routine earlier in the day. Got to basically max alert. Then left and entered the building a few times. When I finally committed myself to staying in the building I started getting turret encounters. I suspect either me going in and out screwed something up. Or how much offense you use to take down the routine determines how long it stays down for.
Turret Monitors / Discussion
This is the discussion related to the wiki page Turret Monitors.