What was found
AIR TURNBACK DUE TO THE LEFT AFT LAVATORY SMOKE DETECTOR SOUNDED SHORTLY AFTER PASSING THROUGH 18,000 FT DURING CLIMB. NO SMOKE OR FUMES WERE OBSERVED. SMOKE DETECTOR SILENCED AROUND 10,000 FT DURING DESCENT. REPLACED AFT LEFT LAVATORY SMOKE DETECTOR. REMOVED DETECTOR DID SOUND OFF SEVERAL TIMES OUTSIDE OF LAV. INSPECTED LAVATORY AND SURROUNDING AREAS. NO DEFECTS NOTED. NO SMOKE OR FUME REPORT BY FLIGHT CREW. PRESSURIZED AIRCRAFT AND PERFORMED NOGO ODI TASK LIST. NO DEFECTS NOTED.