As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PART WAY THROUGH THE FLIGHT THE LAV SMOKE ALARM SOUNDED. INVESTIGATED LAV, THERE WAS NO INDICATION OF ACTUAL SMOKE. SILENCED ALARM BY PUSHING TIP OF A PEN INTO THE RESET HOLE. INSPECTED AND FOUND GREEN LIGHT ILLUMINATED INDICATING NORMAL OPERATION. PERFORMED INSPECTION AND OPS TEST OF FWD LAV SMOKE DETECTOR. NO DEFECTS NOTED. REF FIM 26-12-11-810-801, AND Q400 AMM 26-12-11-710-801.