I was getting tired to remind everyone in the house to keep my door closed/forgetting to close it myself that it inspired me to make this project. 

Items needed:

• Rope (less than 5mm in diameter)
• 2 wall anchors
• 1 Carabiner
• 2 screws (to anchor the carabiner to the door. Like the screws here)
• 1 Ball Bearing (I took mine from the spool holder than came with the Prusa Mini+)
• 1 Water Bottle

Print Suggestions:

• If you get an error in Prusa Slicer saying “The dimensions of the object from file X seems to be defined in meters…” Don't worry, they are to the correct scale. Just select yes and move on.
• Print settings: 0.20mm
• Supports: None
  infill: 20%

Assembly instructions:

1. Print the items.
2. Insert the Ball Bearing into the Pully piece. This may require some force to fit. If you need some help find a hard surface and put the Ball Bearing under the pully piece and press down on it to sandwich the ball bearing into the pully piece. 
3. Push the pully piece onto the Axis piece. 
4. Mount the axis piece onto the wall where you prefer using wall anchors. This should be somewhere close to the upper corner of your door opposite of the hinges.  
5. Use a 3D print like this and mount it to the upper corner of your door opposite of the hinges. You can use other loop 3D prints but I used this and it worked great. Thanks jerry.mahoney for the great print! :D
6. Now take the rope and feed it through the hole at the bottom of the axis piece, through the pully, and out the side hole of the axis piece. 
7. Tie the free end of the rope that you just fed through the axis, to your Carabiner using a knot. Attach the Carabiner to the door.
8. Open your door fully and observe where the rope goes up to on the lower teeth of the axis part. Cut the rope a couple of centimeters below that. (the longer you have it the more chances you have if you mess it up by accident). Check step 11 if you want to double check the length before cutting. 
9. drill a hole in the lid of the water bottle the diameter (or slightly less) of your rope. 
10. feed the rope through the hole in the lid. Using a tooth pick can help quite a bit.
11. Once fed through the lid, Burn the tip of the rope to prevent it from fraying. This can be enough to suspend the bottle by the lid if you are using a plastic base rope. If you are not, tie a knot in the rope so the lid does not slide off. 
12. Fill the water bottle with water and fasten it to the lid. 
13. Test out what you just made. Make sure the door closes. Use a heavier form of weight if it is not closing.