Overwatch
From Combine OverWiki, the English Half-Life Wikia
Overwatch is the general name of the Combine's (presumably automated) Command and Control System on Earth and possibly elsewhere which is most commonly encountered in the form of the Combine Dispatcher / PA.
Overwatch is also the suffix designation of the Combine's military units on Earth, such as Sector 17 Overwatch for City 17 and its surrounding environs.
