TC reported External Smoke Alarm at car1504. Staff(JUR) checked and feedback no sign of smoke or he at.Rear T415 did line clear confirmed no abnormality. ~~~~~ 1504 found external smoke alarm illuminated. Reset & fault did not occur. Swapped fire control panel to #3504. Fire Control Unit S/N : (after Swapped).    #1504 : 008. #3504 : 007.  Jervis/Kana. 14/07/2021.  1504 transferred to RSDBSD to replace smoke detector unit.  Kana. 14/07/2021.   FOLLOW UP OPERATION 10 CHECKED SMOKE DETECTOR UNIT THERE IS SIGN OF WATER INGRESS. REPLACED WITH SPARE. SECURITY/FUNCTION CHECKED DONE OK. AKHBAR/AZHAR 15.07.2021.