In fax and voice data modes, sometimes events occur that the modem wishes to signal to the computer regardless of whether it's in command or data mode. An example of such an event is a caller pressing a touch-tone key in voice mode. Other common out-of-band messages are notifications from the modem that data was lost because the computer is sending data either too slow or too fast, or that the modem hears an unexpected dial-tone on the line (meaning the caller probably hung up), or that the extension handset was picked up or hung up.