Pressure activated linear locking mechanisms and related methods. At least some of the illustrative embodiments are systems including: a cover member defining an inner surface, an outer surface, a length, and a first locking portion; a first hollow defined in the locking portion, the first hollow extending along the length of the cover member; a locking member defining a first appendage extending along a first side, the first appendage defines a cross-section and an internal volume; said first appendage disposed within the first hollow, and when the releasable cover is exposed to atmospheric pressure, the first appendage in an inflated condition; and the first appendage is configured to transition to a deflated condition in response to a predetermined pressure greater than the initial pressure.