This recorder has a special cable that will be connected to the telephone line and will activate automatically when somebody picks up any telephone of that line, to place or receive a call with the voice activation system (VOX) and it will turn off when they hung up. Easy to install on any telephone plug of the line. The DTMF tone decoder is ideal to be used with this recorder, so afrer the recording you can decode the tones of the outgoing calls of that line.