As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAV SMOKE DETECTOR ALARM SOUNDED SHORTLY AFTER TAKEOFF. STOPPED AFTER ABOUT 10 MINUTES. RETURNED TO FIELD WITH NO FURTHER ISSUES.PERFORMED GVI OF LAVATORY, LAVATORY CABINETS AND SURROUNDING AREA. NO EVIDENCE OF FIRE OF SMOKE NOTED. PERFORMED OPS TEST OF THE LAVATORY SMOKE DETECTOR IAW Q400 AMM 26-12-11-710-801. OPS CHECK GOOD. COULD NOT DUPLICATE.