TC reported external fire alarm at car 3673. T426 line clear to BDL2 - no abnormalities. Staff (BSH)boarded T427 - no abnormalities. Staff (NOV) checked and co nfirmed no abnormalities found internal and external. ~~~~~ 3673 blow/clean smoke detectors & function test - OK. No occurrence of fault during monitoring for 1 hr - OK.  Aminur/Isamuddin. 04/11/2020.  3673 found FC 721. Replaced smoke detector unit. Function test & monitor for 2 hrs - OK.  Chan GF/Goh AT. 05/11/2020.