In Genesis, God shut the Ark’s door after Noah and his family entered it.
Genesis 7:16 lists the animals entering the Ark and then states that the Lord shut Noah in. The sentence places the closing of the door under divine action rather than describing Noah fastening it himself.
This detail is easy to confuse with the earlier construction instructions, which tell Noah to make an opening and a door in the Ark. Genesis does not give a mechanical description of the door or explain its locking system. The closing marks the end of preparation and the beginning of the Flood narrative’s period of protection inside the vessel.