TC reported Smoke External Alarm at RearM2 car intermittently. Staff(YCK) checked and confirmed no signs of smoke / fire / burning smell on exterior or interio r of train. Rear T218 line cleared and confirmed no abnormal ~~~~~ T217 3563(N) TC reported Smoke External Alarm at 2563 car intermittently. Staff(YCK) checked and confirmed no signs of smoke / fire / burning smell on exterior or interior of train. Rear T218 line cleared and confirmed no abnormalities. Subsequently at KTB NB, TC reported Smoke External Alarm at 3563 car. Rear T218 line cleared and confirmed no abnormalities. ADM NB CE: T217(3563) check n found this car having smoke external pre-alarm fault. Check no abnormality, reset fault cleared.  #3563 FC-721 smoke external, found smoke detector PCB rusty and sensor dusty, c/o function test ok. #2563 No FC observe, smoke externak detector brand new, clean smoke sensor and function test ok. Done By:Jack/Sanip/Rizman Date:29/10/2023