Abstract: An apparatus for blocking the transmission of echo signals in telephone communications circuits is disclosed. The apparatus employs a voice-activated switch in the transmit channel at each telephone terminal of the telephone circuit to block transmission of signals below a selectable threshold. Under all conditions where received speech signals are present at a telephone terminal, a higher threshold for the switch at that terminal is selected than would otherwise be used to block noise in the channel. This higher threshold is set above the level of the echo signals to prevent their transmission from that terminal by the switch.