The transponder is evolved from the radar IFF system developed by the British Air Force and the United States Army Air Force in the Second World War. In the 1950s, the aviation industry began to use secondary radars to coordinate with transponders for air control of general aviation and commercial aviation.

The core and magnetic tape of the tape recorder are easy to be damaged, and the tape needs to be fed and rewinded repeatedly when querying, so it can not be retrieved quickly. Therefore, this answering machine is not convenient to use and has poor reliability.

The telephone transponder is designed to prevent information and contact omission. It only needs to be very simple and connected to the telephone line, and can automatically answer the phone when the host is not there, and record the content of the call. According to the owner, due to the different models of the answering machine, there are many other very useful functions. The general answering machine is divided into two parts in structure: the owner's message recording and the incoming message recording.