What was found
SHORTLY AFTER TAKEOFF LAVATORY SMOKE ANNUNCIATOR WENT OFF & MASTER CAUTION LAVATORY SMOKE DETECTOR WAS AUDIBLE THROUGHOUT THE CABIN & FLIGHT DECK. FLIGHT ATTENDANTS REPORT AFT RT SMOKE DETECTOR GOING OFF & A GRAY HAZE BEGAN TO FILL CABIN & FLIGHT DECK WHICH DISSIPATED ON LANDING. WARM AREA FOUND INFLIGHT AROUND LAVATORY SMOKE DETECTOR. RT AFT LAVATORY COOLED AFTER LANDING. RAN ENGS 1 & 2 WHILE ISOLATING PACK OPERATION FROM RT TO LT PACK. WHILE DOING SO, CONFIRMED ODOR FROM LT PACK OPERATION. NR 1 PACK PLACED ON DEFERRAL & MEL 21-01 S1. COMPLIED WITH M ACTION, DMI 21596. CLASS C, PLACARDS INSTALLED.