TIMS showed Smoke External Alarm at car1518. Staff(AMK) checked and confirmed no signs of smoke / f ire / burning smell on exterior of train. Rear T409 line cle ar and confirmed no abnormalities. ~~~~~ 1518 TIMS showed Smoke External Alarm. Staff(AMK) confirmed no signs of smoke/fire/burning smell on exterior of train. Rear T409 line clear and confirmed no abnormalities. CE checked: 3518 smoke external alarm reset ok, fault cleared.  3518 found FC 527 (Smoke External). Removed SDR11 relay from fire control panel & isolated smoke detector. OPS 20 raised to check on smoke detector & plaseal.  Jonathan Koh 45051 To check plaseal and smoke detector     Found smoke detector rusty.Replaced and security check and tested ok. Not: 2486512 raise Done by Saini/Asruddin.  06/05/23