Me. Rev. Stat. tit. 25, § 2463-B

Fire suppression sprinklers are not required for an accessory dwelling unit unless the accessory dwelling unit is within or attached to a structure of more than 2 dwelling units, including accessory dwelling units. As used in this section, "accessory dwelling unit" has the same meaning as in Title 30‑A, section 4301, subsection 1‑C.