What characters can Nexmo detect via keypad input?


  • What DTMF characters can be recognized?
  • How does Nexmo handle DTMF tones?
  • Can I collect digits via VXML or TTS?


Using the Voice API, Call API or TTS Prompt API, you can receive keypad input from a user via DTMF. This is processed in 3 different ways:

  1. TTS Prompt API - Capture - We will capture the key input and send this in the callback
  2. TTS Prompt API - Confirm - We will confirm the key input specified and will confirm the PIN was entered correctly or not in the callback using the digits parameter
  3. Using VoiceXML - Used to navigate a menu in the VoiceXML script or to collect digits that you can collect using the <submit> command.

The characters that Nexmo recognises are:

1 2 3 4 5 6 7 8 9 0 * #

# is used to signal the end of DTMF from the user.
e.g. "Enter your PIN code, followed by the # key."
User enters 1234#
You will receive the PIN entered, without the # at the end.

* is interpreted as a . and will be submitted to your server in this format also for Call API.


Please also be careful when building applications for different regions. Some regions will call # the "hash key", while others call it the "pound key". Also, some regions refer to * as the "star key*, while others call it the "asterisk key".

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