As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI INTO IAD, FORWARD CARGO SMOKE DETECTOR LIGHT ILLUMINATED. FLIGHT CREW ACTIVATED FORWARD CARGO BAY FIRE BOTTLE AND DECLARED AN EMERGENCY. AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND NO EVIDENCE OF FIRE OR SMOKE DAMAGE. REPLACED NR 1 CARGO ELECTRONICS UNIT. OPERATIONAL CHECK NORMAL. AIRCRAFT RETURNED TO SERVICE.