a telephone circuit , which may be monolithically integrated , for supplying ringing signals to a subscriber &# 39 ; s telephone line and for detecting an off the hook condition during ringing , including a logic control circuit connected to exchange components which control the supply of the ringing signals and determine their rhythm . the logic control circuit is connected to a circuit for detecting direct current on the line and a current comparator for generating a signal when the value of the line current exceeds a predetermined current value . this signal is also supplied to the exchange components via a transfer circuit to inform them that an off the hook condition has taken place . the logic control circuit is connected to a timing signal generator which synchronizes its functions with times in which the ringing signal has a zero amplitude , and is connected to a signal amplifier circuit which supplies the ringing signals to the line and to the transfer circuit . when the circuit for the detection of direct current signals a probable off the hook condition , the logic control circuit disables the amplifier circuit from supplying ringing signals to the line and inhibits the transfer of any signals to the exchange components , and checks after a predetermined time interval that an off the hook condition has actually taken place .