TC feedback smoke external pre alarm atFront M1 car, station (BGB) checked and feedback no abnormal ities found, Rear Train (T246) line clear also reported backno abnormalities found ~~~~~ TC feedback smoke external pre alarm at     Check and found #1617 water seepage into external smoke sensor unit.Further check surrounding area was no observed any water leak from filter or hatch cover.Replaced smoke sensor unit and functional test ok. Done by Sanip/Koh. 25/04/21