TC reported External Smoke Alarm at car2541. Staff(BSH) checked and feedback no sign of smoke. ~~~~~ 2541 TC reported External Smoke Alarm. Staff(BSH) feedback no sign of smoke.  2541 checked/found Smoke External activated on 17/03/2022 at 0609 hrs. Checked saloon fire panel, no fault indication found. OPS 20 raised to replace External Smoke Detector.  Wong 44638    To change out External smoke detector.     Found smoke sensor PCB gather with water.Replaced smoke sensor and function test ok. Done by Koh/Sanip. 18/03/22