TIMS showed Fire external at car 3548. Staff(KRJ) checked and confirmed no signs fire on exterior orinterior of train. Rear T416 line cleared no abnormalities. ERS-13 ~~~~~ BSD 3548 changeout smoke detector 3548 TIMS showed Fire external. Staff(KRJ) confirmed no signs fire on exterior or interior of train. Rear T416 line cleared no abnormalities. CE 3548 fire external alarm able to reset. No abnormality Depot 3548 smoke detector operational check.  3548 FC 735/721. Checked smoke detector ( #2 end), found water ingress due to gasket missing. Ops-20 raised for smoke detector changeout by BSD.  Alan/Lee PT/Anand 45220