How to make a door automatically lock and unlock without clicking on it?

Hello! I'm sorta stuck here. So picture this, a player enters this room through a door. Once they're in, the door is automatically locked (without clicking on it or some sort) and the player dies due to the monsters I have placed in the room. Once the player dies, the door unlocks itself waiting for the next player. This is what I am trying to accomplish! I can't seem to find any codes or scripts that would do this so I really need your help guys. It would mean a lot ;^;