The Type M-13 Phaser Turret was a formidable type of static defense used by the United Federation of Planets.
They were noted to play an integral part in a colony defensive system. These automated weapons worked in conjunction with a Security Center and the colony's sensor net. This allowed the turret to automatically track and target suspicious or hostile craft within the immediate area. The Type M-13 drew power directly from the phaser banks which were charged directly from the main power grid. A noted problem with the system was that the power phasers were an incredible strain on the colony's resources. This meant that if the power levels exceeded what was available then the turrets autoatically shut down due to insufficient energy.
Ultimately, the phaser turrets were designed to be a deterrent to an enemy. This matched the Federation belief in preventing attacks by a strong display of defensive power. This meant that the turret's pivoted as they tracked targets which reminded aggressors of the costs of a potential assault. (TOS video game: New Worlds)