self - locking parcel delivery box is a container with a special locking mechanism that allows a hinged lid to remain unlocked and openable while the container is empty but then automatically lock shut after a package or parcel has been placed inside and the hinged lid is closed . special locking mechanism comprises , among other things , a rotating striker plate that remains in a closed position while container is empty but then rotates to an open position when a package or parcel is placed inside container . with rotating striker plate in the closed position , a latch cannot extend outward to latch or lock into a latch window when the hinged lid is closed , thereby keeping hinged lid unlocked and openable . with rotating striker plate in the open position , the latch will latch or lock into the latch window when the hinged lid is closed , thereby allowing hinged lid to lock shut .