Question Based on the sugya on daf 9, how does one deal with using a key to open his door on Shabbos, when the area outside is a reshus harabbim? whatis the difference between the door opening into the house or away from the house? Thank you.
When opening a door as you described,The Mishna Berura 346:28 warns to be careful to remove the key form the door after having unlocked it, so as not to transfer the key from one Reshus to another. We are worried that the doorstep itself might have the dimensions of Reshus Hayachid in which case you could not open it outwards or it might not have the dimensions of a Reshus Hayachid which could make it a Carmelis and then you couldn't open it inwards.
So the problem exists regardless of which way the door opens. Some people solve the problem by using mechanical combination locks.
All the best,
Ilan Segal