TC reported Smoke External alarm at front DT car. SM (SOM) checked and confirmed no sign of heat andsmoke on the outside of the train. Rear train T235 did line clear from RFP - CTH NB and found no sign of smoke. ~~~~~ 3714 TC reported Smoke External alarm. SM (SOM) confirmed no sign of heat and smoke on the outside of the train. Rear train T235 did line clear from RFP - CTH NB and found no sign of smoke. CE : Found 3714- Tims showed no smoke external. No abnormality found.  3714 no FC found. Checked/found gasket & cable gland missing from smoke detector cover & terminal cover. Plaseal found still intact. OPS 20 raised to replace missing components & c/o smoke detector.  Lee JC 45181 BSD: To replace 3714 smoke external detector, smoke detector cover gasket, terminal box cover gasket and smoke detector box cable gland.