Blue Box is a simple utility for generating and decoding DTMF (Dual-Tone Multi-Frequency) or touch tones as used in telephone systems. Play back touch tones at adjustable speeds to trigger touch tone operated systems or listen to tones that are being generated and display them. Blue Box also has a red box mode to play 5¢, 10¢ and 25¢ tone combinations that used to be used in US phone systems. Additional tones include dial tone, ring back tone, busy signal, 2600 Hz and a custom tone combination.

Warning: Blue Box is designed as an educational tool and utility. Do not attempt to use Blue for any illegal or malicious purposes. Blue Box can be used to assist in dialing numbers, but can not be used to manipulate digital telephone utility services.

Limitations: Blue Box is software based decoding and is processor intensive. Performance may vary between devices. Tones that are less than 100 ms with pauses that are less than 100 ms are difficult to process in software. Future versions and processors may increase the reliability of faster tone sequences. If you need touch tone decoding for higher speeds, a hardware solution is recommended.

Blue Box can not play tones into the iPhone phone feature while in a call.

Blue Box is useful for entering numbers into touch tone operated systems such as an answering machine passcode or a dial-up service that requires the entering of several touch tones to navigate a menu system. Simply enter the numbers once and then play back the numbers into the phones microphone with a touch.


The interface is as simple to use as a telephone. Simply press a button and it will generate a tone and display the corresponding character. Press the playback button and they will play back.

All graphics were designed for the Retina display on iPhone 4.

Favorites & Contacts

Decode a number you want to keep? Add it to your favorites, where it can easily be accessed and regenerated. Or, load a number for generating tones directly out of the contacts.

Have a number you would like to call? Hold down the dial button when using an iPhone and send the number to the phone feature for dialing.


Various settings provide a way for the user to “tune” Blue Box to suit their generating or decode needs.

Adjust tone length and pause length
Adjust pause character length
Adjust listening trigger threshold
Adjust number of samples for a tone

STEREO/MONO - Play one tone on each channel or play the mixed tones on both channels.

Built-In help file

With a built-in help file, understand how to “tune” Blue Box for particular decoding and generating needs.

What's New

Version 4.1.1

Added the privacy message for microphone use during DTMF decoding. This prevents a crash in iOS10 when the decoding button is pressed.
Minor bug fixes and optimizations.

Ratings and Reviews

All the tones you need


Idk why this didn’t work at first. Without updating it now works. Sorry for the poor initial review!

Waste of time



App Name Misleading


Back in the late 60's and 70's, when AT&T deployed #5 Crossbar switching systems, Blue Boxes were used to emulate the in-band signaling needed to route long distance telephone calls and "surf" the dark unexplored recesses of the long distance telephone network.

#5 Crossbar was phased out and replaced with SS7's "out of band" signaling in the late 70's through early 80's rendering the blue box an impotent artifact of ancient history. Nevertheless, the novelty and folklore of the devices continue to persist.

I would have liked to have rated this app 5 stars, but had to deduct 2.5 stars because the app name erroneously lead me to expect a DTMF encoder that actually emulated the tone matrix of a true "Blue Box" on the iPhone. When the author includes the correctly tuned matrix in the app I'll update my rating. There's no longer any applicable reasons not to (and haven't been for almost 3 decades).

I also had some difficulty with the decoder and subtracted a half point for failing to buffer the touch tone strings detected by the software to work around the frequency detection / number identification issues.

Otherwise, the app does everything else it claims, and the ability to adjust pulse and interval lengths was a nice touch.

Please fix the frequency encoder and allow the user to switch between Blue Box DTMF and "standard" DTMF.


Sunshine Valley Systems
10.6 MB
Requires iOS 8.0 or later. Compatible with iPhone, iPad, and iPod touch.
Age Rating
Rated 4+
© 2010 Sunshine Valley Systems


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

More By This Developer

You May Also Like