A device for providing security and environmental protection to an individual telephone subscribed pair having an appearance at a building entrance terminal. The device prevents unauthorized removal of an R.J. 11 plug, and selectively closes the opening leading to a corresponding R.J. 11 jack. In one embodiment, a sliding door is fixed upon a mounting plate and is secured in position by a simple tumbler type lock. In another embodiment, the lock itself includes integrally formed flanges that perform the same function as the sliding plate. In still another embodiment, the plate is substituted by a small padlock hasp.