Use a door wedge or rubber stopper under the door
Tie the door handle to a heavy, immovable object
Use a belt, rope, or cord to secure the handle to a fixed point
Place a chair under the doorknob if the door opens inward
Slide a bar, broom handle, or metal rod through the handles if possible
Use a portable door security bar
Stack heavy furniture against the door
Use a door jammer or security brace
Secure the door with adhesive hooks and strong cord
Use a carabiner or clip to connect the handle to a fixed anchor point