I like the systems where housekeeping uses the room phone to notify their in-house system that the room has been cleaned and I'm presuming there is a code that it is vacant. That should stop the FD from checking someone else in before the room is ready. Of course that presumes no one gets into the room after that. I especially hate properties the leave the rooms open (flip lock or block the door) while they move from room to room. I've had movie charges show up hours after I left the properties. I takes a while to get management to back those out.