As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SMOKE ALARM WENT OFF IN AFT LAV. NO SMOKE OBSERVED AND FLIGHT LANDED UNEVENTFULLY. SUPPLEMENTAL DATA UPDATE THE AFT CENTER LAV SMOKE DETECTOR WAS AT FAULT. THE UNIT WAS REPLACED WITH P/N PU90-461R3 (PCN 563-3542) . THE SYSTEM CHECKED FINE AFTERWARD.