A weapons locker was a storage area for firearms aboard Federation starships, shuttlecraft, and outposts. These lockers were typically accessed through a simple touch interface or voice command to authenticate authorized access by Starfleet personnel.
Depending on the purpose and size of a weapons locker, it could store phasers, phaser rifles, portable weapons containers, and other standard Starfleet personnel equipment. Phaser rifles were regularly stored with the muzzle facing upwards for ease of retrieval, and phasers were placed in a manner in order to optimize storage space. (Star Trek: First Contact; Star Trek VI: The Undiscovered Country)
Although most weapons lockers were placed in strategic locations such as in armories, near transporter rooms, shuttlebays, or security offices, certain starships, such as the Constitution-class USS Enterprise-A, had a weapons locker in the kitchen. (Star Trek VI: The Undiscovered Country)
A weapons locker was also located in the staging area aboard the USS Enterprise, before and after the 2270s refit. (TOS: "The Cage"; Star Trek: The Motion Picture) In 2266, the Enterprise also included a weapons locker on H deck. (TOS: "The Conscience of the King")
In 2266, Lieutenant Kevin Riley broke into the weapons locker on H deck of the Enterprise and stole a phaser from it, intending to use the weapon to murder Anton Karidian. (TOS: "The Conscience of the King")
In 2369, Tosk tampered with an access terminal in a corridor on Deep Space 9 in an attempt to access a weapons locker located in the habitat ring, level five, section three. (DS9: "Captive Pursuit") Chief Miles O'Brien and Major Kira Nerys also took advantage of similar weapons lockers aboard Deep Space 9. (DS9: "Hard Time", "Shattered Mirror")
For the weapons lockers seen on Star Trek: Deep Space Nine, real-life containers were used but were modified so that it was not visible on screen that they had previously served another function. In "Hard Time", however, Chief O'Brien opens a locker and some letters can be seen on the inside of the lid; those letters were not made unreadable. On the screenshot to the right (turned 180 degrees and mirrored), the words "Action Packer" are legible. In real life, "Action Packer" is a line of storage containers by Rubbermaid.