Md. Code, Public Safety § 12-1104

(a) Except as provided in subsections (b) and (c) of this section, there must be a carbon monoxide alarm installed in a central location outside of each sleeping area within a dwelling subject to this subtitle.

(b) For a hotel or a lodging or rooming house, on or after April 1, 2017, there must be a carbon monoxide alarm installed within the dwelling, as follows:

(1) on the wall inside each guest room that:

(i) contains a device that emits carbon monoxide;

(ii) is adjacent to a room or area that contains a device that emits carbon monoxide;

(iii) is adjacent to an enclosed unventilated attached garage; or

(iv) is connected by ductwork to an enclosed unventilated attached garage or room or area that contains a device that emits carbon monoxide; and

(2) on a wall in each room or area that:

(i) contains a device that emits carbon monoxide;

(ii) is adjacent to a room or area that contains a device that emits carbon monoxide; or

(iii) is adjacent to an enclosed unventilated attached garage.

(c) For a rental dwelling unit, on or after April 1, 2018, there must be a carbon monoxide alarm installed within the dwelling as follows:

(1) outside and in the immediate vicinity of each separate sleeping area; and

(2) on every level of the unit, including the basement.

(d) Notwithstanding subsections (a), (b), and (c) of this section, if there is a centralized alarm system that is capable of emitting a distinct and audible sound to warn all occupants, the owner of a dwelling may install a carbon monoxide alarm within 25 feet of any carbon monoxide–producing fixture and equipment.