What was found
REPEAT WRITE-UP, DURING PREFLIGHT AND AFTER BAGGAGE FIRE TEST WAS COMPLETED WE GOT RED BAGGAGE FIRE CAS AND A RED BAGGAGE FIRE PUSH BUTTON ILLUMINATED. APU SHUT DOWN. RAN CHECKLIST BUT DID NOT DISCHARGE FIRE BOTTLE. WENT TO VIZUALLY INSPECT BAGGAGE BAY, NO FIRE PRESENT BUT A VERY THIN HAZE OF SMOKE NOTED. LEFT BAGGAGE DOOR OPEN. AND RETURNED TO COCKPIT. SOME TIME AFTER MY RETURN THE RED BAGGAGE FIRE CAS WENT OUT AS DID THE RED BAGGAGE FIRE PUSH BUTTON. REPLACED BAGGAGE COMPARTMENT SMOKE DETECTOR IAW AMM 26-13-05. OPS CHECK GOOD.