N.Y.C. Admin. Code § 28-312.4: § 28-312.4 Periodic replacement of smoke alarms.

Smoke alarms required pursuant to section 907.2 of the New York city building code or sections 27-978, 27-979, 27-980 and 27-981 of the 1968 building code shall be replaced when the time elapsed since the installation of such alarm exceeds the manufacturer's suggested useful life of the alarm.

Exception: A smoke alarm installed before April 1, 2014 and whose end of useful life is not known shall be replaced with an alarm that complies with section 28-312.5 by no later than April 1, 2021.