JavaScript Blue Box

A blue box was an electronic device that hackers once used to generate "phone tones", beeps and chirps to illegally place long distance calls thru the phone lines. Such a device would not work today. But we can still produce those tones for fun and record them. And this page can also translate those tones back into numbers! It provides a JavaScript DTMF encoder and decoder that runs entirely in the browser. The blue box encoder generates authentic DTMF dialing sounds using the Web Audio API, while the decoder analyzes live audio from the microphone, and it can analyze uploaded sound files to detect numbers dialed. No server-side processing — everything runs client-side, in the browser for privacy, and to save our bandwidth.

Dual-Tone Multi-Frequency (DTMF) is the signaling system behind touch-tone telephone dialing. Every key on a phone keypad produces a unique pair of simultaneous tones — one from a low-frequency group (697, 770, 852, 941 Hz) and one from a high-frequency group (1209, 1336, 1477, 1633 Hz). The combination of these two tones identifies each key (0–9, *, #, A, B, C, D) and with luck, can be detected by our DTMF decoder.

DTMF was introduced by AT&T around my birthday in 1968 and quickly became the global standard for in-band dialing, replacing single-frequency pulse dialing. It is used not only for telephone dialing but also in voicemail systems, IVR menus, telephony APIs, and even some radio and amateur communication systems. So if you recorded some tones off the radio and want to know the digits, you have come to the right place.

Important Disclaimer. This DTMF decoder and tone generator is provided for educational or entertainment purposes only. The software active on this page comes with NO WARRANTIES. Not even the implied warrantee of merchantability or fitness for any purpose whatsoever. The author retains copyright and publication rights under the Apache License. All other rights, risks, and responsibilities belong to the user. Looking for work. If you are serious about development, hire an expert programmer who can take your project to the next level. Other stuff. Use the menu at left to browse more JavaScript toys, games, and widgets: Speak in binary, long number calculator, more calculators, JavaScript editor, DAW, eye test, image blocks, fontfun, block art, snow, amaze, artify, and the online games on our Windows PC support website. Keep it going. Support development or hire an expert programmer for your next project.