As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - CLIMBING THROUGH 18,000 FEET, THE MASTER WARNING AND SMOKE WARNING LIGHTS CAME ON FOR ABOUT 3 SECONDS, THEN THE SMOKE LIGHT WENT OUT. VISUAL CHECK OF THE BAGGAGE COMPARTMENT FOUND NO EVIDENCE OF SMOKE OR FIRE. REPLACED THE NR 2 SMOKE DETECTOR. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.