TIMS showed Smoke External Alarm at car2511. Staff(YCK) checked and confirmed no signs of smoke / f ire / burning smell on exterior or interior of train. Rear T 201 line clear and confirmed no abnormalities. ~~~~~ TIMS showed Smoke External Alarm at car 2511. Staff(YCK) checked and confirmed no signs of smoke / fire / burning smell on exterior or interior of train. Rear T201 line clear and confirmed no abnormalities.  2511 FC 721, Check and found smoke detector sensor mushroom    dirty, clean and function test ok Done by faiz, khalid, Kamal 13.09.23