Abstract: An intercom system for a door and inside stations has a speech function for two-way communication with hands-free operation. The intercom system includes a two-wire connecting lead between the door station and each inside station to transmit a conversation current and an operating current. The intercom system includes a bridge circuit for suppressing feedback, a bipole circuit to decouple conversation currents from a power supply, a calling circuit for calling on the two-wire connecting lead and using a call current of opposite plurality with respect to the operating current, and a short-circuit circuit in each inside station for short-circuiting the corresponding two-wire connecting lead when the corresponding door opening button is actuated.