As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAV SMOKE MASTER WARNING IN CRUISE. F/A VERIFIED THAT PASSENGER BUMPED HIS HEAD ON AFT LAV CEILING NO SMOKE FOUND IN LAV. MASTER WARNING/MESSAGE DURATION ABOUT 30 SECONDS. REMOVED FROM SERVICE. PERFORMED GVI OF LAV SMOKE DETECTORS, NO DAMAGE NOTED. COMPLIED WITH LAVATORY SMOKE DETECTOR TEST, PER E175 AMM TASK 26-14-01-70-801-A. NO DEFECTS NOTED. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.