TIMS showed Smoke External Alarm. Staff(BSH) checked and confirmed no signs of smoke / fire / burnin g smell on exterior or interior of train. Rear T237 line cle ar and confirmed no abnormalities. ~~~~~ TIMS showed Smoke External Alarm. Staff(      Checked TIMS found #3553 and #3554 smoke external faults. Checked both external smoke detector units, found them to be dusty. Cleaned both smoke detector units with compressed air and cleaned surrounding area with clean cloth. Checked cable glands with plaseal on units ok. Function test ok. Done by: Sanip, Koh (17/1/24)