As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A PASSENGER WENT INTO LAV R3, CLOSED THE DOOR AND A SMOKE DETECTOR AURAL ALERT WAS OBSERVED IN THE COCKPIT. FLIGHT ATTENDANTS CONFIRMED FALSE WARNING. ACCOMPLISHED LAVATORY SMOKE DETECTION SYSTEM GROUND SCANNING AND NO FAULTS FOUND. LAV SMOKE DETECTION SYS OPS CK GOOD IAW MM 26-17-00.