Missile turrets used to rely on sensor towers and radar towers to detect enemy units. However, by the GDC 2008 build they could detect by themselves. By May 21st, 2009 they had lost their detection ability again. Missile turrets were detectors again at the start of the StarCraft II beta. During the Legacy of the Void beta, missile turrets lost the engineering bay requirement for their construction. This was reinstated, as the developers felt that the change didn't spark a change in strategy, and that "the choice to just build Turrets easily didn’t feel like a good add to the game."