The StarCraft II website was updated with the second Terran building that Blizzard is showing off: the Sensor Tower. This tower appears to offer a new detection mechanism for the Terran forces, but it's currently unknown if the Missile Turret will retain its detection functionality as well, or if it was ripped out of the turret and introduced through this new tower.

As the screenshots below show, the detection range extends beyond the visual range of the tower and other buildings, so it can even detect units into the fog of war itself. This is enhanced by an octagonal shape with an exclamation mark in the middle, signifying incoming enemy troops. Check out the official Sensor Tower page to see short clips of the tower in-game.