He is talking about someone that is "keeping your door open" and Ari is the one that opens the door sometimes.
Both Ari and Maddie open the door.
Ari checks for a little bit through the right door and nobody can kill you through that door while she is checking then leaves after a little bit.
Maddie gets on the door, forces it open and you can still get killed through it and will only leave if you interact with the microwave.