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What is DTMF?

DTMF (Dual-Tone Multi-Frequency) is the technology behind keypad input on the phone. When a caller presses a key on their phone (0-9, * or #), a tone signal is sent that your voice assistant can detect and process. With the DTMF tool, your voice assistant can react to these keypad inputs — e.g. to accept a PIN entry, offer a menu, or ask for a customer number.

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When should I use DTMF?

  • PIN or code entry: When callers need to enter a sequence of digits (e.g. customer number, confirmation code)
  • Menu selection: “Press 1 for sales, 2 for support, 3 for accounting”
  • Confirmations: “Press 1 to confirm or 2 to cancel”
  • Confidential data: When information should not be spoken out loud (e.g. passwords, account numbers)

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Create a DTMF tool

  1. Open the Voice Wizard for your voice assistant
  2. Switch to the Tools tab
  3. Click Add and select DTMF Input
  4. Give the tool a unique name (e.g. dtmf_pin, dtmf_menu)
  5. Choose the desired input mode (see below)
  6. Click Save
Note: The name of the DTMF tool must be unique and may only contain letters, numbers, underscores, and hyphens. Use a descriptive name, e.g. dtmf_pin for a PIN prompt or dtmf_menu for a menu selection.

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Input modes

Depending on your use case, three different input modes are available:

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How does DTMF input work during a conversation?

Once a DTMF tool is enabled for your voice assistant, the assistant automatically detects keypad input throughout the entire conversation. The flow is as follows:
  1. The voice assistant prompts the caller to press keys (e.g. “Please enter your PIN”)
  2. The caller presses the corresponding keys on their phone
  3. The assistant detects the entered digits and processes them
  4. The assistant responds accordingly — e.g. it transfers the caller or gives a confirmation
Good to know: Keypad input is detected throughout the entire call, not just at a specific point in time. The assistant receives the entered digits automatically.

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DTMF and subprompts

If your voice assistant works with intents and subprompts, you can enable the DTMF tool selectively at specific levels:
  • A DTMF tool on the main prompt is available during the corresponding conversation phase
  • You can enable a separate DTMF tool with its own settings on a subprompt
  • Each prompt in the hierarchy can enable or disable DTMF tools independently
Note: If you enable a tool on a prompt that contains subprompts, the activation only applies to that specific prompt. Subprompts require separate activation if DTMF is needed there as well.

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Practical examples

Assistant: “Welcome to Example Corp. Press 1 for sales, 2 for support, or 3 for accounting.” Caller: presses key 2 DTMF input detected: “2” — the call transfer tool forwards the caller to a person Assistant: “You have chosen support. I’ll connect you with an agent.”Setting: mode “Single digit”
Assistant: “Please enter your 4-digit PIN.” Caller: presses 7 3 9 1 DTMF input detected: “7391” — API request to the backend for PIN verification Assistant: “Thank you. Your PIN has been verified successfully.”Setting: mode “Fixed length”, number of digits: 4
Assistant: “Please enter your customer number and confirm with the pound key.” Caller: presses 5 8 3 2 1 0 # DTMF input detected: “583210” — API request to the CRM system with the customer number Assistant: “Thank you. I received customer number 583210. One moment please, I’ll look up your data.”Setting: mode “Variable length”

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Frequently asked questions

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Can I create multiple DTMF tools for one voice assistant?

Only one DTMF tool can be active at a time per prompt level. To use a different DTMF tool, disable the existing one first. Across different subprompts, however, you can use different DTMF tools — e.g. a menu tool on the main prompt and a PIN tool on a subprompt.

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Which keys are supported?

All standard phone keys: 0-9, * (star) and # (pound).

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Does DTMF also work on mobile phones?

Yes, DTMF works with all phones — landline, mobile, and VoIP devices. The caller needs to open the phone keypad during the call and press the desired keys.

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Can the assistant respond to DTMF input and speech at the same time?

Yes, the assistant can process both spoken input and keypad input. Both input channels can be used in parallel.