Abstract: A ring-down or non-dial subscriber telephone such as a freeway emergency telephone is connected to automatic electronic switching (EAX) equipment for interconnection with an emergency operator by an interface circuit having a polarity-sensitive full-wave bridge controlling voice connection of the telephone to the operator. Actuation of the bridge is controlled by a current sensitive controller connected in series with the originating loop containing the freeway telephone. The bridge monitors the on-hook and off-hook states of the called telephone and energizes alarm circuitry upon failure of the calling telephone to go on-hook within a predetermined time after the called telephone goes on-hook. The circuit also has a capability of monitoring current flow in the originating loop containing the calling telephone and of energizing a common alarm circuit in the EAX equipment in the absence of such current flow.