A self-aligning locking device for a vehicle sliding door assembly includes a sliding door threshold configured to be mounted on a door panel. The threshold is configured to slide along a sliding axis. The threshold includes a latch and a tongue at a car body-engaging end of the latch. The locking device also includes a groove block and a hook plate both configured to be coupled to the car body. Optionally, the locking device can include a switch sensor. The tongue of the threshold is configured to engage the groove to maintain alignment of the hook plate to mate with the latch to lock the threshold to the car body. The optional switch sensor can be configured to generate a signal indicating a locked state of the hook with the latch responsive to actuation of the switch sensor by the latch.