A busy signal (or engaged tone) in telephony is an audible or visual signal to the calling party that indicates failure to complete the requested connection of that particular telephone call.

  • a reorder tone, (sometimes called a fast busy signal), indicates that no transmission path to the called number is available.
  • an otherwise unspecified busy signal indicates that the called number is occupied or otherwise unavailable
  • this tone sometimes occurs at the end of a call to indicate the other party has hung up.

Many different countries have different signalling tones that act as "busy signals".