As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 4377 - DURING CLIMB-OUT, CREW NOTED LAVATORY SMOKE DETECTOR WARNING IND. VERIFIED NO SMOKE IN LAVATORY. CREW RETURNED TO ORD. NO EMERGENCY DECLARED AND NO OVERWEIGHT LANDING REPORTED. AIRCRAFT LANDED SAFELY, NO FURTHER INCIDENTS REPORTED. REMOVED AND REPLACED NR 2 DAU AND LAVATORY SMOKE DETECTOR IAW AMM. OPS CHECK GOOD. (M)