DTMF (Dual-tone multi-frequency) is an in-band telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment, other communications devices, and switching centers. The tones are decoded on the receiving end and used for practical applications such as interacting with computer systems and answering machines. The interaction with a computer system is achieved using an IVR (Interactive voice response) system.

Over a regular landline, DTMF is sent as audio signals & the tones are transmitted through the same wires that carry the voice signals. In the case of mobile phones, DTMF tones can be generated only after the connection is established.

How do we use it?

This feature is often used by call centers for gathering inputs from callers for the selection of IVR menus, capturing account information for phone banking facilities, and so on, however, this is prone to errors such as echo or packet loss during transmission, distorting the data and making it difficult to rebuild the keypress combination at the receiving end.


One of the ways our clients use the Last-mile delivery solution is by triggering calls programmatically via the ExoPhone, digits# tuple (Ex: 08033013302,12345#) & often times, we see them reach out to us inquiring as to why DTMF doesn’t always get captured.


In this case, the call flow would roughly have the following applet(s) -

Gather > Passthru > Connect


Gather > Connect

Note that while these call flows always start with a Gather applet, the way DTMF works and what have been our findings will hold good even for the normal IVR use-cases as well.

Troubleshooting with DTMF

Find more information here in case your application is observing issues with DTMF.

If you have any questions or concerns, please connect with us using the chat widget on your Exotel Dashboard or Whatsapp us on 08088919888