Alerting device for telephones
First Claim
1. An alerting device for connection to a telephone line and a telephone device, said alerting device comprising:
- a voice circuit for connection between the telephone line and the telephone device, said voice circuit including a current limiting resistor for series connection between the telephone device and the telephone line;
an alarm circuit for generating an alarm;
a current monitoring circuit connected to said voice circuit for detecting the presence of current in said voice circuit, said current monitoring circuit being operatively connected to said alarm circuit for providing a first triggering signal to said alarm circuit when current is present in said voice circuit; and
a voltage monitoring circuit for connection to said telephone line for detecting when the voltage across said telephone line drops below a threshold value, said voltage monitoring circuit being operatively connected to said alarm circuit for providing a second triggering signal to said alarm circuit when said voltage is below said threshold value,wherein said alarm circuit will generate said alarm when it receives said first triggering signal and said second triggering signal simultaneously.
1 Assignment
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Accused Products
Abstract
A telephone alerting device for connection to a telephone line and a telephone. When the telephone is off-hook, the device will generate a visual and an audio alarm if an additional telephone connected to the same line also goes off-hook, thereby providing an eavesdropping alarm. The audio alarm is a periodic signal of short duration heard in the ear-pieces of all off-hook telephones connected to the telephone line. The device includes a voice path having a resistor placed in series with the telephone for raising the voltage across the telephone line when the telephone alone is off-hook. In order to trigger the alarm, the telephone must be off-hook and the voltage across the telephone line must be below a threshold value.
37 Citations
20 Claims
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1. An alerting device for connection to a telephone line and a telephone device, said alerting device comprising:
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a voice circuit for connection between the telephone line and the telephone device, said voice circuit including a current limiting resistor for series connection between the telephone device and the telephone line; an alarm circuit for generating an alarm; a current monitoring circuit connected to said voice circuit for detecting the presence of current in said voice circuit, said current monitoring circuit being operatively connected to said alarm circuit for providing a first triggering signal to said alarm circuit when current is present in said voice circuit; and a voltage monitoring circuit for connection to said telephone line for detecting when the voltage across said telephone line drops below a threshold value, said voltage monitoring circuit being operatively connected to said alarm circuit for providing a second triggering signal to said alarm circuit when said voltage is below said threshold value, wherein said alarm circuit will generate said alarm when it receives said first triggering signal and said second triggering signal simultaneously. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An alerting device for connection to a telephone line having tip and ring lines and a telephone device, the alerting device comprising:
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a voice circuit for connection between the telephone line and the telephone device, said voice circuit including indicating means for indicating when a current is passing through said voice circuit and current limiting means for limiting the current through said voice circuit; a monitoring circuit comprising telephone line monitoring means for detecting when the potential across said telephone line drops below a predetermined value;
voice circuit monitoring means responsive to said indicating means for detecting when a current is passing through said voice circuit; and
an alarm means for indicating an alarm when said line monitoring means detects that said potential is below said predetermined value and said voice circuit monitoring means detects that current is passing through said voice circuit;coupling means for coupling said monitoring circuit between said tip and ring lines. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. An alerting device for connection to a telephone line and a telephone device, the alerting device comprising:
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a voice circuit for connection between the telephone line and the telephone device; an alarm circuit for generating a signal on said telephone line that causes an audio sound to be generated by the ear-pieces of the telephone device and other off-hook telephone devices connected to the telephone line; a current monitoring circuit connected to said voice circuit for detecting the presence of current in said voice circuit, said current monitoring circuit being operatively connected to said alarm circuit for providing a first triggering signal to said alarm circuit when current is present in said voice circuit; and a voltage monitoring circuit for connection to said telephone line for detecting when the voltage across said telephone line drops below a threshold level, said voltage monitoring circuit being operatively connected to said alarm circuit for providing a second triggering signal to said alarm circuit when said voltage is below said threshold, wherein said alarm circuit will generate said signal only when it receives said first triggering signal and said second triggering signal simultaneously. - View Dependent Claims (17, 18, 19, 20)
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Specification