Patent ID: 8180033

Claim:
A telephone line monitoring device, connected to a telecommunications network via a telephone line, and adjacent to a telephone device using the telephone line, for preventing the telephone line from being used illicitly, the telephone line monitoring device comprising: a rectifying circuit for generating a corresponding direct current voltage according to an effective voltage of the telephone line; a first controller for generating a first control signal when the direct current voltage is lower than or equal to a predetermined voltage; a second controller for detecting an operating state of the telephone device and generating a second control signal when the telephone device is being operated; a load booster for pulling down the effective voltage of the telephone line when enabled; and a first switch circuit for disabling the load booster when receiving the second control signal, and enabling the load booster when receiving the first control signal while not receiving the second control signal; wherein the first controller comprises a sampling circuit, a comparator, and a reference voltage circuit; the sampling circuit is connected between the rectifying circuit and an inverting input terminal of the comparator, the reference voltage circuit is connected to an non-inverting input terminal of the comparator, and an output terminal of the comparator is connected to the second controller and the first switch circuit.