TIMS showed Smoke External Alarm at car3609. Staff(AMK) checked and confirmed no signs of smoke / f ire / burning smell on exterior or interior of train. Rear T 412 line clear and confirmed no abnormalities. TIMS showed S ~~~~~ #3714 smoke external alarm. Preventively replaced smoke detector unit. Notification no: 2548100 Done by: Zulfikri and Haikel