Importance

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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.

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First Claim