DTMF Code

What is a DTMF Code?

Dual-tone Multi-frequency code or DTMF is a response code that is created when the end user presses the numbers on a mobile or landline phone’s keypad. All numbers are identified in a unique way with the DTMF code that can be transferred and interpreted on the receiver side. DTMF code signaling allows reception of information from the end user e.g. PIN code during a voice call. Voice systems like BSG's Conversational AI Voice read DTMF input when callers respond via keypad.

Each number from 0 to 9 is uniquely identified with a DTMF code that can be received and interpreted on the receiver side. DTMF code signaling enables the reception of information from the end user e.g. PIN codes during a voice call.

DTMF is also how callers respond to automated menus over regular phone lines, independent of any SMS or messaging channel. For real-world context, see BSG's How to Measure the Success of Your Voice Bot Implementation – BSG Guide 2024.

How does it work?

When a user presses a number on a telephone keypad, the switch in the telephone exchanges sends a signal containing two tones to the phone. The two tones are composed of two frequencies: a low-frequency tone and a high-frequency tone. Each tone represents a number or symbol. The switch in the telephone exchange then reads the combination of these two frequencies and converts it into a signal that is sent to the telephone. This signal is then interpreted by the telephone as the inputted number or symbol.

How are DTMF codes used in the Telecom industry?

Smartphones today use a digital process for standard calling and messaging, so DTMF codes are not used when connecting to the mobile network base station. However, they do support DTMF codes for a number of important use cases:

• Entering pin codes as part of 2FA authentication solutions
• Entering credit card details over the phone
• Navigating automated telephone menu systems
• Integrations with older telephone systems