TIMS showed Smoke External Alarm at RearDT. Staff(AMK) checked and confirmed no signs of smoke on i nterior of train. Rear T405 line clear and confirmed no abno rmalities. ~~~~~ TIMS showed Smoke External Alarm at Rear Check and found external ISD sensor very dusty,c/o as preventive measure.Function test ok. #3549-external FSD:    Not: 2494556 raise. Done by Sanip/Koh. 04/06/23