TIMS showed Smoke External Alarm at FM1car 1515. Staff(AMK) checked and confirmed no signs of smoke/ fire / burning smell on exterior or interior of train. Re ar T255 line clear and confirmed no abnormalities. TIMS show ~~~~~ 1515 TIMS showed Smoke External Alarm. Staff(AMK) checked and confirmed no signs of smoke  / fire / burning smell on exterior or interior of train. Rear T255 line clear and confirmed no abnormalities.  1515 FC 721 registered. Found wire connector & gasket cover missing. It was temporarily sealed with rubber plaster. Currently no water or dust ingress in the device. OPS 20 Raised. To replace smoke external device. Sugu/Anand 45188 BSD: To replace smoke detector   OPS20: Replaced 1515 external smoke detector unit. Security check ok, function test ok. Notification to CSC: 2527606 Done by: Saini, Haslan (28/9/23)