(2) Smoke alarms required in one- and two-family dwellings constructed before July 1, 1975, shall be battery powered or alternating current (AC) primary electric powered units.

(3) Smoke alarms required in one- and two-family dwellings constructed between July 1, 1975, and June 30, 1990, shall be alternating current (AC) primary electric powered units.

(4) Smoke alarms required in multifamily residential occupancies including apartments, lodging or rooming houses, dormitories, and hotels shall be alternating current (AC) primary electric powered units.

(5) Smoke alarms required in a residential occupancy constructed on or after July 1, 1990, shall be alternating current (AC) primary electric powered units with battery backup or an approved alternate secondary power source.

(b) At least one smoke alarm shall be installed in each level of a residential occupancy constructed on or after January 1, 1989, including basements and excluding unoccupied attics, garages, and crawl spaces.

(c) If two or more smoke alarms are required within a residential unit constructed on or after January 1, 1989, the smoke alarms shall be arranged so that activation of any one smoke alarm causes alarm activation of all other required smoke alarms within the residential unit.

(d) (1) Subject to paragraph (2) of this subsection, smoke alarm placement in a one- or two-family dwelling shall be upgraded to comply with paragraph (3) of this subsection in existing residential occupancies when any one of the following occurs:

(i) the existing smoke alarms exceed 10 years from the date of manufacture;

(ii) the existing smoke alarms fail to respond to operability tests or otherwise malfunction;

(iii) there is a change of tenant in a residential unit and the residential unit has not previously been equipped in accordance with this subtitle with sealed long-life battery smoke alarms with silence/hush button features within the 10 years preceding the change of tenant; or

(iv) a building permit is issued for an additional residential unit or alteration to a residential unit.

(2) Smoke alarm placement shall be upgraded to comply with paragraph (3) of this subsection in all existing residential occupancies on or before January 1, 2018.

(3) Upgraded smoke alarm placement shall include the following:

(i) a minimum of one smoke alarm on each level of the residential unit, including basements and excluding unoccupied attics, garages, and crawl spaces;

(ii) smoke alarms shall be alternating current (AC) primary powered units with battery backup, except as follows:

1. smoke alarms in one- and two-family dwellings constructed before July 1, 1975, may be battery operated; and

2. smoke alarms required in new locations by this section, if smoke alarms did not previously exist, may be battery operated; and

(iii) if battery operated smoke alarms are permitted, only sealed, tamper resistant units incorporating a silence/hush button and using long-life batteries may be used.

(e) In one- and two-family dwellings, a smoke detector installed as a part of an approved household fire alarm system is an acceptable alternative to the AC powered-battery backup smoke alarms required by this section, if the smoke detectors are installed and located as specified in subsection (a) of this section.

(f) A smoke detector installed as a part of an approved fire alarm system is an acceptable alternative to the AC powered-battery backup smoke alarms required by this section, if the smoke detectors are installed and located as specified in subsection (a) of this section.