The utility model discloses an audible and visual alarm based on liquid crystal device, including casing and fiber coupler, fiber coupler includes a fiber coupler, the 2nd fiber coupler and the 3rd fiber coupler, and sets up respectively at under and lateral wall of the left side of casing wall, right side wall, outside the casing is all placed in to one of them port of every coupler among the fiber coupler, is provided with HPDLC grating and TN device in the casing, the utility model discloses novel structure is unique, during adoption liquid crystal device is applied to the optical fiber measurement, has advantages such as the optical loss is little, short response time, has optical device's accuracy, and whether can effectually detect the lightguide cable link remote site before the OTDR test has optical signal input, judges whether remote site equipment breaks off, has avoided high -power light signal direct output to the optical equipment worn -out fur transmitting terminal because of OTDR, leads to the incident of equipment damage.