(a) The requirements of this article shall apply to any dwelling unit in existence on January 1, 1989. Except as provided in subsection 17-5(b), the smoke detectors required in such dwelling units may be either battery powered or wired into the structure's AC power line, and need not be interconnected.
(b) In the case of any dwelling unit that is newly constructed, reconstructed or substantially remodeled after January 1, 1989, the requirements of this article shall apply beginning on the first day of occupancy of the dwelling unit after such construction, reconstruction or substantial remodeling. The smoke detectors required in such dwelling unit shall be permanently wired into the structure's AC power line, and if more than one detector is required to be installed within the dwelling unit, the detectors shall be wired so that the actuation of one detector will actuate all the detectors in the dwelling unit.