Automatic bridge defense system

The automatic bridge defense system, as its name suggests, is a computer-controlled defensive phaser weapon found on the bridge of Federation starships around 2269.

When a malevolent lifeform took control of the USS Enterprise (NCC-1701) in 2269, it tried to use the system to force the crew's obedience. 

Background information
When this defense system is introduced in the script of "Beyond the Farthest Star", the script dictates that the system is to be "hereinafter referred to as BDS", though this abbreviation is never used anywhere else in the teleplay. The beams are identified as phasers in the script. The system's activation is discribed: "A small ball-shaped object protrudes from a ceiling hatch. It has a full field of fire all around the bridge if necessary, and it is armed with phaser mechanisms. We will see it as needed."