Monitor for preventing fraudulent use of telephone line

The utility model relates to a monitor for preventing fraudulent use of telephone lines, which belongs to the technical field of communication circuits. The utility model can be connected between a telephone and telephone lines in series in the mode of a junction box, and the utility model can also be arranged in the telephone to form a whole with the telephone. The utility model is characterized in that when the telephone lines are in fraudulent use, control circuits in the interior part cause dc short-circuit or ac short-circuit between two lines of the telephone, the telephone in fraudulent use can not be dialed out, and sound and light alarm is given simultaneously. The utility model has the advantages that the complete machine has minimal power consumption; under normal condition, batteries can be used for a plurality of years; the current that the telephone lines consume is not more than 5 mu A; the dc impedance effect on the telephone lines is not more than 1 omega, and accordingly, the utility model does not cause harmful effects on conversation lines.