DTMF (Dual-Tone Multi-Frequency) is the signaling system that generates tones when phone keypad buttons are pressed. These tones enable touch-tone input for navigating menus, entering numbers, and providing responses during calls.
How does DTMF work?
Each keypad button produces a unique combination of two audio frequencies. The receiving system detects these tones and interprets them as digit inputs. DTMF works reliably across phone networks because the tones travel through the same audio channel as voice.
Why does DTMF matter for voice AI?
While voice input is primary for AI agents, DTMF remains valuable for certain inputs. Account numbers, PINs, and credit card numbers may be more accurately captured via keypad than speech. Some callers prefer keypad input for sensitive data or in noisy environments. Supporting both input methods improves accessibility.
DTMF in practice
An AI agent asks for a callback number. The caller can either speak the digits or enter them on their keypad. For sensitive verification codes, the agent says: “Please enter your PIN using your phone keypad.” This hybrid approach combines conversational ease with precise numeric capture.