Da Voismart Knowledge Base.
Listen to a channel, and optionally whisper into it

  ChanSpy([chanprefix][|options]): This application is used to listen to the
audio from an Asterisk channel. This includes the audio coming in and
out of the channel being spied on. If the 'chanprefix' parameter is specified,
only channels beginning with this string will be spied upon.
  While spying, the following actions may be performed:
    - Dialing # cycles the volume level.
    - Dialing * will stop spying and look for another channel to spy on.
    - Dialing a series of digits followed by # builds a channel name to append
      to 'chanprefix'. For example, executing ChanSpy(Agent) and then dialing
      the digits '1234#' while spying will begin spying on the channel
    b             - Only spy on channels involved in a bridged call.
    g(grp)        - Match only channels where their ${SPYGROUP} variable is set to
                    contain 'grp' in an optional : delimited list.
    q             - Don't play a beep when beginning to spy on a channel, or speak the
                    selected channel name.
    r[(basename)] - Record the session to the monitor spool directory. An
                    optional base for the filename may be specified. The
                    default is 'chanspy'.
    v([value])    - Adjust the initial volume in the range from -4 to 4. A
                    negative value refers to a quieter setting.
    w             - Enable 'whisper' mode, so the spying channel can talk to
                    the spied-on channel.
    W             - Enable 'private whisper' mode, so the spying channel can
                    talk to the spied-on channel but cannot listen to that