TIMS showed Smoke External Alarm at RearM2 car 2561. Staff(BSH) checked and confirmed no signs of s moke / fire / burning smell on exterior or interior of train . Rear T216 line clear and confirmed no abnormalities. ~~~~~ 2561 TIMS showed Smoke External Alarm. Staff(BSH) checked and confirmed no signs of smoke/fire/ burning smell on exterior or interior of train. Rear T216 line clear and confirmed no abnormalities.  2561 found FC 721 (Smoke External) on TIMS. Checked/confirmed no sign of smoke/fire/burning smell. Removed SDR11 relay & isolated smoke detector function on FCP. OPS 20 raised to check external smoke detector & plaseal.  Jonathan Koh 45085 TO CHECK PLASEAL & EXTER L SMOKE DETECTOR Replacement done on the above mention reported and fix back SDR11 relay. Security check and tested ok.Monitor for few hrs ok. Smoke detector unit:- Not: 2497058 raise. Done by Saini/Haslan/Asruddin.  12/06/23