As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR - CREW REPORTED LEFT AFT LAVATORY SMOKE ALARM WENT OFF ON DESCENT. FLIGHT LANDED LHR WITHOUT INCIDENT. INSPECTED A5 LAVATORY FOR EVIDENCE OF FIRE AND NONE FOUND. REPLACED LEFT AFT LAVATORY SMOKE DETECTOR. SYSTEM GROUND CHECK NORMAL OPERATION.