TIMS showed Smoke External Alarm at car2549. Staff(YCK) checked and confirmed no signs of smoke / f ire / burning smell on exterior or interior of train. Rear T 223 line clear and confirmed no abnormalities. ~~~~~ 2549 TIMS showed Smoke External Alarm. Staff(YCK) confirmed no signs of smoke/fire/burning smell on exterior or interior of train. Rear T223 line clear and confirmed no abnormalities. CE : Smoke external alarm reset ok.  2549 FC 721. Checked/found external smoke detector no water ingress/water marks, no dust clog, wiring condition, cable gland & plastercine - OK. Found smoke detector terminal side gasket missing. Swapped FCP from #2549 to #2550. Function test - OK. OPS 20 raised to replace missing terminal gasket.  Sarma/Sugu/Anand 45094 FCP S/N : (after swapped) #2549 : 164 #2550 : 167