What was found
SEA - AFTER TAKEOFF, SMOKE DETECTOR IN LAVATORY SOUNDED. FLIGHT ATTENDANT OBSERVED A LIGHT HAZE IN CABIN. AFTER 4 MINUTES THE SMOKE DETECTOR STOPPED, HAZE DISAPPEARED. AFTER LANDING, GROUND RUN AIRCRAFT AT POWER, CYCLED NR 1 PACK, NOTICED ACRID SMELL. WITH NR 1 OFF, NO ACRID SMELL. PLACED NR 1 PACK ON MEL. AT BOI, REMOVED AND REPLACED NR 1 PACK. OPERATIONAL CHECK GOOD.