EMB120 ACFT WHILE TAXIING HAD LAVATORY SMOKE DETECTOR SOUND; THEN QUIT. CABIN ATTENDANT CHKED LAVATORY AND FOUND NO SMOKE OR FIRE. FLC NOTIFIED GND CTLR THAT THEY WOULD NEED TO STOP FOR MAINT. DETECTOR WENT OFF AGAIN AND CABIN ATTENDANT THOUGHT SHE MAY HAVE SMELLED SOMETHING. CAPT ELECTED TO EVAC THE ACFT. CAUSE OF WARNING UNKNOWN.

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TAXIING FOR DEP; LAVATORY SMOKE DETECTOR SOUNDED; THEN QUIT. INITIALLY; FLT ATTENDANT CHKED LAVATORY AND FOUND NO INDICATION OF SMOKE OR FIRE. CAPT ASKED ME TO NOTIFY GND CTL THAT WE WOULD NEED TO PULL OFF THE TXWY AND CALL MAINT. SMOKE DETECTOR SOUNDED AGAIN. THIS TIME; FLT ATTENDANT SAID SHE COULD SMELL SOMETHING; POSSIBLY SMOKE. CAPT MADE DECISION TO EVAC THE ACFT ON THE TXWY; WHICH I RELAYED TO GND CTL. FLT ATTENDANT INSTRUCTED PAX TO LEAVE THEIR CARRY-ON'S ON THE ACFT AND EXIT THROUGH MAIN CABIN DOOR. I EXITED WITH THE PAX PER CAPT'S INSTRUCTIONS TO HELP KEEP EVERYONE IN AN AREA AWAY FROM THE ACFT. ALL PAX AND CREW EXITED ACFT SAFELY. CFR ARRIVED ON SCENE WITH ARPT SECURITY. NO EVIDENCE OF SMOKE OR FIRE WAS IMMEDIATELY EVIDENT AT THE SCENE. LAVATORY SMOKE DETECTOR WAS ONLY RECENTLY INSTALLED ON THIS TYPE ACFT. PRIOR TO THIS TIME; NO DETECTOR OR EXTINGUISHERS WERE INSTALLED IN THE ACFT LAVATORY. WHEN SMOKE DETECTOR WAS INSTALLED; COMPANY ADDED PROC FOR INFLT SMOKE OR FIRE EMER. SINCE THIS EVENT OCCURRED ON GND; CAPT FOLLOWED EMER EVAC PROCS.