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Fold Accordion app icon: a small brown accordion with bass buttons, red bellows and piano keys

Fold Accordion

A musical instrument built for iPhone Duo. The hinge is the bellows.

For iPhone Duo and every iPhone. Coming Fri Oct 23.

Fold Accordion on an open iPhone Duo playing Ode to Joy. Bass and chord buttons sit on the left edge, piano keys on the right edge, and red bellows stretch across the fold. The D bass button and the E key are lit.
Open iPhone Duo, playing Ode to Joy. Keys at the edges, bellows across the fold.

How you play

Demo with sound, 37 seconds: pumping the bellows with the iPhone Duo hinge, a song that plays itself, the Fold / Swing / Touch picker, and Swing on iPhone. Recorded in the iOS Simulator.

Work the bellows to push air, and press the keys on screen to pick the notes. Move faster to play louder. A quick change of direction dips the air, like a real bellows.

Fold

iPhone Duo

Open and close the phone to push air. On an open Duo, the keys sit at the outer edges and the bellows cover the fold, stretching as the hinge opens. Fold it shut and swinging takes over.

Swing

Every iPhone

Swing the phone side to side to pump the bellows. Pull one way, push the other.

Touch

Every iPhone

The air flows while you hold a key. No folding or swinging. Just play with your fingers.

Pick Fold, Swing or Touch from the badge at the top of the screen, or in Songs. Fold is offered on iPhone Duo only.

Keys, bass and chords

  • Right-hand piano keys from C4 to G5.
  • Six bass notes and six chords on the left: F, C, G, Dm, Am, Em.
  • Play several keys at once.
  • Stop moving and the sound stops.

Recorded accordion sound

The sound is a real accordion, recorded note by note.

Songs that play themselves

Four public-domain songs play themselves, with the keys lighting up as they go. The melody is on the piano keys; the bass side plays oom-pah.

Let the song work the bellows, or pump along yourself. Turn off Auto bellows and the song keeps its own time while you supply the air. Turn off Lock keys to play along on the keys.

  • Ode to Joy Ludwig van Beethoven
  • When the Saints Go Marching In Traditional
  • Oh! Susanna Stephen Foster
  • Jingle Bells James Lord Pierpont

Screenshots

Tap a screenshot to open it at full size.

Open iPhone Duo in Fold mode. The header reads Fold and unfold to play, with a Fold badge and a half-full air meter. Bass and chord buttons on the left edge, piano keys on the right edge, red bellows across the middle.
iPhone Duo, Fold mode. The air meter fills as the hinge moves.
The Songs sheet on iPhone Duo: Ode to Joy, When the Saints Go Marching In, Oh! Susanna and Jingle Bells, then a Bellows picker with Fold, Swing and Touch, and a Lock keys switch.
Songs, and the Fold / Swing / Touch picker.
Ode to Joy playing on iPhone Duo with an Auto badge. The D bass button and the E key are lit.
A song plays itself and lights the keys it presses.
Dark mode on iPhone Duo, playing Jingle Bells. The C chord button and the C4 key are lit.
Dark mode, playing Jingle Bells.
iPhone in Swing mode. The header reads Swing to play with a Swing badge and the air meter partly full. Bass and chord buttons on the left, narrow bellows in the middle, piano keys on the right.
iPhone, Swing mode.
iPhone in Touch mode. The header reads Touch the keys to play with a Touch badge.
iPhone, Touch mode.
iPhone playing Oh! Susanna. The C chord button and the E key are lit.
iPhone, playing Oh! Susanna.

Screenshots from the Xcode simulator (iPhone Duo and iPhone 18 Pro), taken Oct 2, 2026.

Accessibility

  • Touch mode plays with fingers only. No folding or swinging.
  • VoiceOver names each key by its note, bass or chord, in the app's language.
  • VoiceOver reads the bellows and the air meter as percent.
  • Songs can play hands-free.
  • Light and dark mode.

Languages

The app is in English and 11 other languages:

  • English
  • Deutsch
  • Français
  • Italiano
  • Español
  • Português (Brasil)
  • Nederlands
  • Polski
  • 日本語
  • 한국어
  • 简体中文
  • 繁體中文

Note names follow the language musicians there use: Do Re Mi in French, Italian and Spanish; H for B in German and Polish; letters everywhere else.

Privacy

Fold Accordion makes no network connections. No analytics, no ads, no account, no in-app purchases. Your settings are stored on your phone.

Fold Accordion privacy policy

Support

Questions, bugs or ideas? Email us.

spatial@specialglasses.net
  • iPhone only. Needs iOS 27 or later.
  • Fold mode needs an iPhone Duo. Swing and Touch work on every iPhone.

Accordion recordings: “Cellini Accordion” by Miles_Thompson on Freesound, CC0 1.0. Reed synthesizer adapted from Accorduon by Artem Novichkov, MIT License. Full texts are in the app's Acknowledgements screen.