A B737-700 FLIGHT CREW EXPERIENCED A FRONT LAVATORY SMOKE ALARM. THEY DECLARED AN EMERGENCY AND RETURNED TO LAND AT THEIR DEPARTURE AIRPORT.

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THE ACFT'S APU HAD BEEN WRITTEN UP A COUPLE OF TIMES. MOST RECENTLY IT APPARENTLY SELF-DESTRUCTED AND WAS DEFERRED. I DON'T KNOW IF IT HAD BEEN 'RUN' BY MAINT THE NIGHT BEFORE; BUT ON OUR ORIGINATING FLT; THE LOGBOOK HAD A FUEL USED BY MAINT ENTER OF 200 OR 300 LBS. I MENTION THIS FOR LATER COMMENTS. WE WERE CLBING OUT WITH A LEVELOFF AT 9000 FT FOR TFC. THE FRONT LAV SMOKE ALARM STARTING SOUNDING AND THE FLT ATTENDANTS CALLED US ON THE FLT INTERPHONE TO NOTIFY US. AFTER A SHORT CONVERSATION; I DECLARED AN EMER; REQUESTED THE FIRE EQUIP TO MEET US; AND TURNED BACK TOWARD ZZZ. WE LANDED OPPOSITE DIRECTION ON RWY AND THE FIRE EQUIP ACCOMPANIED US TO THE GATE. PLEASE ACCEPT SOME OBSERVATIONS FOR CONSIDERATION: FROM THE TIME THE ALARM SOUNDED TO TOUCHDOWN ON RWY WAS APPROX 5 MINS. AS I DETECTED NO SMOKE OR FUMES; I CALLED FOR THE CABIN/LAV FIRE CHKLIST. WE WERE SO BUSY THAT WE HAD NO CHANCE TO COMPLETE IT. (NOR; WITH THE INFO I HAD AVAILABLE AT THE TIME; DID I THINK IT WAS CRITICAL. I JUST WANTED TO GET THE ACFT ON THE GND BEFORE THINGS GOT BAD.) I THOUGHT PULLING THE LAV SMOKE DETECTOR CIRCUIT BREAKER WOULD DISABLE THE CREW CALL SYS; SO I LET THE THING SOUND. NOT TRUE YACK LIPS; THAT IS ONLY THE CLASSIC ACFT. IN ADDITION; THE NOTE TALKING ABOUT THIS IS AT THE BOTTOM OF A FULL PAGE OF ADDITIONAL INFO/CONSIDERATIONS IN THE QRH (CLASSIC AND NEXT GEN BOTH). MIGHT WANT TO MAKE THAT MORE USER FRIENDLY. ALSO; I BELIEVE THE LAV SMOKE DETECTOR LOCATION AS DESCRIBED IN THE CLASSIC QRH IS IN ERROR. LASTLY; THAT CIRCUIT BREAKER SHOULD HAVE A BLUE COLLAR ON IT TO EXPEDITE FINDING IT. IT'S RIGHT BEHIND THE CAPT'S L BUTT CHEEK WHICH MAKES IT A CONTORTION FOR THE CAPT AND IMPOSSIBLE FOR THE FO TO REACH. SO FINDING IT IS ONE THING; PULLING IT IS A CREW ENDEAVOR.