What was found
AT ALTITUDE, GOT A FIRE BOTTLE LOW ANNUNCIATOR. CREW RAN QRH & DECLARED AN EMERGENCY. FIRE DEPART CHECKED ACFT & OBSERVED NO EVIDENCE OF FIRE. THERE ISN'T A WAY TO VERIFY WHICH FIRE BOTTLE WOULD HAVE TRIGGERED ANNUNCIATOR. FOUND NO CASS MESSAGE AT ARRIVAL TO ACFT, PERFORMED A GVI OF LT & RT ENGS FOR EVIDENCE OF HAYLON DISCHARGE. NO DEFECTS. PERFORMED GVL OF LT & RT FIRE BOTTLES & APU FIRE BOTTI.ES WITH NO DEFECTS. PERFORMED FIRE TEST, PASSED, RAN BOTH ENGS FOR 30MIN & COULD NOT DUPUCATE. HCC REQUESTED WEIGH BOTTLES TO DETERMINED IF DISCHARGED. REMOVED FWD & AFT ENG FIRE BOTTLES. FOUND AFT NR 2 BOTTLE 1 LB LESS THAN LAST HYDRO TEST. R & R AFT NR 2 FIRE BOTTLE. VISUAL CHECKED GOOD. IAW MM 26-21-01.