TC reported Master fault light illuminated and TIMS showed rear DT smoke external alarm. Pax was dis embarked at ORC2. Staff(ORC) checked and confirmed that no s ign of heat and smoke at rear DT car. TC also confirmed when ~~~~~ #3543 Fault code 721 smoke external. Tried to reset button but no avail. Swap control panel from #3543 to #1543, fault remain at #3543. Checked by Zulqarnain. 28/03/20. Checked and found #3543 no. 2 end smoke detector unit faulty. Replaced and carried out smoke function check ok. Done by Jack/Sateesh/Koh   30/03/20.