As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI THE CREW GOT A LAVATORY SMOKE DETECTOR INDICATION. CRASH-FIRE-RESCUE MET THE AC AT THE GATE AND THE PASSENGERS WERE DEPLANED. MECHANIC INSPECTED THE AC AND FOUND NO INDICATION OF FIRE OR SMOKE. MECHANIC REPLACED THE OXYGEN/ECS WITH APU PANEL AND RETURNED THE AC TO SERVICE. (K)