What was found
CREW REPORTED AFTER TAKEOFF, F/A NOTIFIED CAPTAIN OF LAV FIRE ALARM GOING OFF. THERE WAS NO FIRE, NO ODOR, AND NO SMOKE NOTED. THERE WAS ALSO NO COCKPIT INDICATION OF SMOKE. CREW DECLARED AN EMERGENCY AND RETURNED TO THE FIELD WITHOUT INCIDENT. ACFT REMOVED FROM SERVICE. PERFORMED HIGH POWER RUN WITH FLIGHT CREW AND CHECK LAV FOR ANY SMOKE ODOR INDICATION, NO SMOKE OR ODOR NOTED, PERFORMED OPS CHECK OF LAV SMOKE DETECTION SYS, OPS CHECK NORMAL. ACFT RETURNED TO SERVICE.