self-locking (adjective)

1. The sculpture had a self-locking mechanism that made it stay upright when the pieces were assembled.

2. Why did the door become a comedian? Because it had a self-locking mechanism that always closed with a punchline!

3. In the suspense movie, the murderer used a self-locking door to trap the protagonist inside the room.

4. The mystery novel featured a secret room with a self-locking door, which played a crucial role in solving the crime.