Abstract: A telemetering system useful for telephone installations. A normally open switch is placed between the line and telephone set. A ringing signal permits sensing apparatus to deliver a coded message to the line between the first and second rings, and the normally open switch is closed before the second ring. Ordinarily calls are delayed for the period of one ring and calls seeking data collection are disconnected before the normally open switch closes. Alternatively data may be delivered to a station associated with the telephone set.