Audible signaling device for informing when a telephone line is available or in use

摘要

A device is provided for connection to a shared telephone line for detecting and audibly indicating the on-hook and off-hook status of the line. The device includes sensing and changing circuitry connected to the shared telephone line for detecting a voltage step occurring during status change transitions between on-hook and off-hook states and correspondingly changing the device during these status changes transitions so that the device is prohibited from drawing power from the shared telephone line when the shared telephone line in not in use. A piezo speaker produces audible on-hook and off-hook sights corresponding to on-hook and off-hook states of the telephone line.