As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT HAD INDICATION OF SMOKE IN LAV AND FIGHT ATTENDANT REPORTED A BURNING SMELL. CAPTAIN DECIDED TO RETURN AS A PRECAUTION AND DECLARED AN EMERGENCY. AC LANDED WITH NO ISSUES, MAINTENANCE WAS NOTIFIED AND CALLED TO THE GATE. MAINTENANCE FOUND THE LAV SMOKE DETECTOR TO BE AT FAULT. REMOVED AND REPLACED THE LAV SMOKE DETECTOR PER THE EMB 175 AMM, OPS CHECKED GOOD. AC WAS RELEASED BACK INTO SERVICE.