As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF FROM DTW, THE AFT LAVATORY SMOKE DETECTOR WENT INTO ALARM AND THE CABIN WAS REPORTED TO HAVE SMOKE IN IT. FLIGHT RETURNED TO THE FIELD AND LANDED WITHOUT INCIDENT. NO EMERGENCY EVACUATION. MAINTENANCE WAS UNABLE TO DUPLICATE THE SMOKE. A DIVERTER VALVE DUCT WAS FOUND TORN AND HAS BEEN REPLACED AND BOTH WATER SEPARATOR COALESCER BAGS HAVE BEEN REPLACED. THE AIRCRAFT HAS RETURNED TO SERVICE.