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