TC reported 'External Smoke Pre-Alarm #1set' at FDT car. Staff (CBR) chceked and confirmed no abnor malities. ~~~~~ 3714 TC reported 'External Smoke Pre-Alarm #1 set. Staff(CBR) chceked and confirmed no abnormalities.  3714 checked external smoke detector no water ingress/stain in the detector. Cleaned the external pre-alarm smoke detector - Done. Function test - OK. ER D/L & no abnormal fault found.  Chan GF/Selvan/Alcus 44137