TIMS showed Smoke External Alarm at car3570. Staff(AMK) checked and confirmed no signs of smoke / f ire / burning smell on exterior or interior of train. Rear T 256 line clear and confirmed no abnormalities. ~~~~~ 3570 - TIMS showed Smoke External Alarm. Staff(AMK) confirmed no signs of smoke/fire/burning smell on exterior or interior of train. Rear T256 line clear and confirmed no abnormalities.  3570 Checked FC 721 Smoke External. No other records found on other dates. Smoke detector checked rubber gland & gasket - OK. Found base plate cover found crack, unable to tighten screw. Top cover not fully covered. SDR11 swop from #3570 to #1570 for monitoring. Operation 20 for smoke detector changeout.  Aliff/Daniel 45259  CAR #3570 REPLACED SMOKE EXTER L UNIT.CONDUCTED FUNCTION TEST OK.SECURITY CHECKED OK.M HAIRUL/ZOHRI 09.12.2023