TIMS showed Smoke External Alarm at car3501. Staff(BNL) checked and confirmed no signs of smoke, fi re or burning smell on exterior or interior of train. Rear T334 line clear and confirmed no abnormalities. TIMS showed S ~~~~~ * ,N * 3501 smoke external unable to duplicate in depot. From TIMS registered FC721 (Smoke external) occurred once and reset ok. Checks shows no sign of water ingress or water seepage at fire panel. Further check on the smoke detector found old signs of water seepage. Able to see rust. Raised OP20 to TWD to c/o smoke detector. DONE BY: SHANKAR/RAZALI 09.05.23   3501 :Replace external smoke detector unit. Security & Function checked-Ok.   Zahir / Fazli / Shafian.  13.05.2023. Smoke Detector Old S/No: Nil. Noti to RSW- 2488243.                New S/No: KSFSD-05.