Chicago code;
13-64-130 Smoke detectors – Location.
Not less than one approved smoke detector shall be installed in every single-family residential unit and multiple dwelling units as defined in Chapter 13-56, Sections 13-56-020, 13-56-030 and 13-56-040. The detector shall be installed on the ceiling and at least four inches from any wall or on a wall located from four to 12 inches from the ceiling, and within 15 feet of all rooms used for sleeping purposes, with not less than one detector per level, containing a habitable room or unenclosed heating plant.
13-64-150 Smoke detectors – Standards.
All approved smoke detectors herein required shall be either the ionization chamber or the photoelectric type and shall comply with Chapters 14-8, 14-16 through 14-36 and 14-44 through 14-72* of the municipal code of Chicago. Detectors shall bear the label of a nationally recognized standards testing laboratory that indicates that the smoke detectors have been tested and listed as a single or single and multiple station smoke detectors. All approved smoke detectors installed in buildings hereafter erected shall be permanently wired to the electrical service of each dwelling unit in accordance with the provisions of Chapters 14-8, 14-16 through 14-36 and 14-44 through 14-72* of the municipal code of Chicago.
CO2 Detectors:
13-64-210 Carbon monoxide detectors – Location.
Not less than one approved carbon monoxide detector shall be installed in each residential unit. The detector shall be installed within 15 feet of all rooms used for sleeping purposes.
No where in the code does it say the CO2 detectors have to be tied into the smokes. The code also does not even say the CO2 detectors need to be hardwired. There are exemptions which you should read carefully.
