As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX-ON CLIMBOUT SMOKE ALARM WENT OFF IN LAVATORY THROUGH 5,000 AGL. NO SMOKE WAS VISIBLE IN COCKPIT OR CABIN. REPLACED LAVATORY SMOKE DETECTOR AND NR 2 ENGINE GROUND RUNS CHECK GOOD, NO LEAKS NOTED, NO SMOKE PRESENT. AIRCRAFT RETURNED TO SERVICE.