MD80 FLT CREW HAS REPEATED MOMENTARY CARGO FIRE WARNINGS DURING CRUISE; DISCHARGES FIRE BOTTLE AND LANDS.

Narrative

WE WERE ALERTED TO AN UNKNOWN ALARM IN THE COCKPIT WHILE ON THE GND DURING BOARDING IN ORD APPROX 20 MINS PRIOR TO DEP. IT WAS A MOMENTARY BEEPING OF WHICH THE DURATION DID NOT EXCEED 2 SECONDS. UNABLE TO SPOT ANYTHING OBVIOUS; I PRESSED TO TEST THE CARGO FIRE TEST BUTTON AND THAT SEEMED TO DUPLICATE THE WARNING. WE OBSERVED THE CARGO DOORS WERE OPEN AND FIGURED IT MUST HAVE BEEN AN ERRONEOUS WARNING. ENRTE TO DCA ANOTHER MOMENTARY WARNING NOT EXCEEDING 2 SECONDS. THIS TIME WE SPOTTED THE AFT CARGO LIGHT JUST BEFORE THE WARNING STOPPED. WE ASKED THE FLT ATTENDANTS TO BE ALERT BUT NOTHING MORE HAPPENED AND WE ARRIVED DCA WITHOUT FURTHER INCIDENT. ON MY WALKAROUND IN DCA I SPENT SOME TIME OBSERVING THE AFT CARGO HOLD FOR ANYTHING AT ALL ABNORMAL. NOTHING NOTED. RPTED SAME TO CAPT. ON DSCNT INTO ORD; WARNING ALERTED US INTERMITTENTLY AGAIN (AFT CARGO). AGAIN WE ASKED FLT ATTENDANTS TO BE ALERT AND CHKED QRH. ALTHOUGH WE AGREED IT WAS A FAULTY ALERT WE DISCHARGED A BOTTLE AND PROCEEDED WITHOUT FURTHER INCIDENT TO ORD. MAINT MET US ON ARR AND CONFIRMED ALERTS TO BE FROM A MALFUNCTIONING SYS.