You should have a minimum of one smoke detector on each level of the home and in the hallway outside of the bedrooms. However, new codes require that smoke detectors be installed in the following manner:
1. There is to be one smoke detector installed in each bedroom.
2. If the ceiling height in the living room is more than 2 feet higher than the ceiling height in the hallway, there must be a smoke detector installed in the living room.
Fire Department – Home Safety Information