State statutes require that functional detectors must at the minimum have batteries replaced before a tenancy begins. If a detector is non-functional, it must be repaired or replaced. If a tenant is occupying the property, repairs to/replacements of smoke and carbon monoxide detectors MUST be completed quickly by law. https://www.ncleg.net/EnactedLegislation/Statutes/HTML/ByArticle/Chapter_42/Article_5.html https://www.ncleg.gov/EnactedLegislation/Statutes/PDF/ByArticle/Chapter_42A/Article_5.pdf