As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: SPURIOUS LAVATORY SMOKE WARNING DURING CRUISE. FLIGHT ATTENDANT REPORTED IT CAME FROM MID LAVATORY. THERE WAS NO SMOKE AND NO PERSON HAD USED THE LAVATORY. PERFORMED TSM TASK 26-17-00. NO CURRENT FAULTS. INSPECTION OF MID LAVATORY SMOKE DETECTOR FOUND CONTAMINATED FILTER, CHANGED SMOKE DETECTOR FILTER.