simple automatic door closer

This is a very simple note to help you keep your heat in the warm room you like.
If the rest of your family likes to open the door and release all the warmth you desperately want to stay in the room, then you may find the use of this little hacker.
All you need is a thick rubber band and two pushpins.
You will stick the pin in the wooden door and the door.
So make sure you have permission to do so.
Stick a pin on the door frame a bit far from the door, and to some extent the rubber band does pull the pin out.
You can do this at the top of the door, but I chose to do it at the bottom.
The second pin is placed on the door so that the rubber band is stretched when the door is opened.
Stick it inside and test if it can close your door, if not then move it down and use stronger rubber bands, or more rubber bands.
You can also try to oil the door hinge to help it move smoothly and reduce some friction.
There is no exact scientific basis for this, so try it, good luck.