Let your voice agents listen, capture, and respond to keypad inputs from users — essential for collecting sensitive inputs like phone numbers and PIN codes securely and efficiently. DTMF (Dual-Tone Multi-Frequency) support ensures your agents can handle numeric inputs with precision, whether it’s authenticating users or routing calls based on input.

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What is DTMF and Why Enable It?

DTMF is a system that sends numeric input over phone lines — like when you enter a PIN, press “1 for support”, or key in an account number. With DTMF enabled, your voice agents can collect:
  • Phone Numbers
  • PIN Codes
  • Account Numbers or OTPs
Why it matters:
  • Secure Input: Collect sensitive information without relying on voice transcription.
  • Better UX: Give users a familiar way to respond via dial pad.
  • Essential for IVR: Key component of any interactive phone workflow.
  • Improves Accuracy: Ideal for situations with background noise or low-quality audio, where speech recognition may struggle.

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How to Enable DTMF Support

You’ll find a toggle under Agent Settings → Customize → DTMF Collection.
⚠️ Important: Simply turning on the DTMF toggle does not activate the full flow.
To make it work, you must also update your system prompt using the correct DTMF signals as shown below.

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DTMF Collection Template

Update your system prompt with the following format when collecting inputs. The signal format must be precisely followed.

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Collecting Phone Number

When your agent asks for a phone number:
  • Append this signal: | DTMF1010
  • Ask the user clearly to provide input after the beep
  • Input must be a 10-digit number (e.g., 8197800293)
System Prompt Example:
“Can you please provide your phone number after the beep tone? | DTMF1010”
If the input is invalid:
“That doesn’t seem like a valid phone number. Please enter a 10-digit phone number after the beep. | DTMF1010”

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Collecting Pin Code

When your agent asks for a PIN:
  • Append this signal: | DTMF0610
  • Input must be exactly 6 digits (e.g., 560033)
System Prompt Example:
“Can you please provide your pin code after the beep tone? | DTMF0610”
If the input is invalid:
“That doesn’t seem like a valid pin code. Please enter a 6-digit pin after the beep. | DTMF0610”

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How DTMF Signals Work

DTMF signals follow the format:
| DTMF[XXYY]
Where:
  • XX = Expected number of digits
  • YY = Time (in seconds) allowed for user input
For example:
  • DTMF1010 → Expect 10 digits, allow 10 seconds
  • DTMF0610 → Expect 6 digits, allow 10 seconds
⚠️ Tip: Always set the YY duration based on the TTS utterance length.
If the message is long but the time is short, the input might timeout before the beep.

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💡 Bonus Tips & Best Practices

TipWhy It Helps
Match time to utterance lengthIf the YY value (input time) is too short for your message, users won’t be able to respond in time.
Don’t strip or reformat DTMF signalsThey must remain at the end of the prompt exactly as written.
Handle invalid input loopsGuide the user to retry if their input doesn’t match the expected format.
Use clear instructionsMention “after the beep” to guide user expectations and ensure input is captured.
Enable barge-in (optional)If you’re using TTS, enabling barge-in allows users to enter input without waiting for the entire prompt to finish.
Validate inputs post-callYou can log or validate the collected digits after the call for reporting or verification workflows.
Use in noisy environmentsDTMF ensures input collection even when speech transcription is unreliable due to background noise.
By enabling and correctly using DTMF, you open up powerful, secure, and user-friendly workflows for your voice agents — from authentication to onboarding and beyond. Let your agents hear more than just voices. Let them listen to actions.