When used in this act:
(a) "Dwelling unit" means a single-family residence, multiple-family residence and each living unit in a mixed-use building.
(b) "Smoke detector" means a device or combination of devices which operate from a power supply in the dwelling unit or at the point of installation for the purpose of detecting visible or invisible particles of combustion. Such term shall include smoke detectors approved or listed for the purpose for which they are intended by an approved independent testing laboratory.